Watching “Broadway: The American Musical,” the six-hour PBS special that traces the form’s rises and falls over the last century, I was both happy and sad. Happy that the show was visiting one of my favorite cultural neighborhoods; unhappy that it chronicled so many losses, and that so many of them seemed to be concentrated in the most recent decades.

Let me back up a bit, and also reassure you that this won’t be one of those “Oh, you should have been there on opening night in 1937, they-just-don’t-make-‘em-like-they-used-to” essays. They don’t, and we all just need to accept that and move on.

And sometimes it’s good that they don’t. For example, the first episode of the series talked about performers using blackface. This was a totally accepted, even expected, part of many major musical stars’ routines (not just Al Jolson’s) — shiny coal-black faces framing collagen-thick lips and bugged-out eyes as singers dropped to one knee and belted a paean to their Mammy down in Alabammy. The documentary made the point that if these performers and songwriters were allowed (or wanted) to sing about their own actual experience, most would have donned a yarmulke and sung about their Yiddishe mama from Lithuwannia.

In other words, the Jewish/immigrant energy that fueled musical theater through about 1940 was being cross-pollinated with, and literally masked by, the native black/American entertainment of the minstrel show and its blackface traditions. That made sense, but blackface still squicks me out. I turned to my boyfriend and said “I just don’t get it; there must have been something audiences saw and accepted then, on whatever level, that we just can’t comprehend now. In 50 years people will look at our obsession with reality television the same way.” But I digress.

In the last hours of the documentary, which was directed by Michael Kantor and written by Marc Fields, Kantor and Laurence Maslon, the losses begin to mount, beginning with the horrifying roll call of AIDS deaths. One commentator, Stephen Mo Hanan, noted that in the years before AIDS became a (mostly) chronic illness and not a death sentence, it took not only musical theater’s “generals” — skilled, even visionary directors like Michael Bennett and Ron Field — well before their time, but also the infantry of musical theater: the worker bees who dare to dream as they execute a dance step, paint a flat, sew a costume or belt a song.

The documentary also included incredible footage of Jonathan Larson (writer/composer of Rent) on his last day working as a waiter at Soho’s Moondance Diner. His death just prior to the first Off-Broadway previews of Rent was a tragedy not only for him and his loved ones but for musical theater (although the cynical part of me noted that it probably helped propel a worthy show into the spotlight). You can count on the fingers of one hand the musicals that have successfully combined rock music and an actual downtown sensibility with the storytelling needs and expectations of a Broadway musical, and Rent is one of those few.

There may be other Jonathan Larsons out there — and the documentary pointed out that his family has started a foundation to encourage them — but his death, like that of the similarly young George Gershwin, who died in 1937 at age 38, left a gaping hole. We won’t get the chance to know if Larson was a genius on Gershwin’s level. But the really sad thing is that Gershwin, at his death, had already written at least a score of musicals — shows that had been produced and performed and seen and applauded. Rent was, if I’m not mistaken, one of the first shows that Larson was able to get on the boards. Something is wrong with this picture.

That something is money. Money money money. Producer-director Hal Prince, another of the documentary’s talking heads, said he and his partners had to raise $250,000 to produce The Pajama Game in 1954. In 1971, when he produced and co-directed Stephen Sondheim’s Follies, it was the most expensive musical to date, with 500-plus elaborate costumes, a complex scenic design and a huge cast. According to Prince, it cost $800,000.

Fast-forward to today and Wicked, another elaborate costume-and-effects show, which cost $14 million to produce. So in the 17 years between 1954 and 1971, the cost of producing a musical increased about two and a half times. But in the following 33 years, instead of increasing by five times, the cost increased MORE THAN 14 TIMES. If ordinary consumer products followed this rate of inflation, a gallon of milk would cost in the neighborhood of $40, and a movie ticket would cost $100 — about as much as an orchestra seat for a Broadway musical (these last are guesstimates, I’m not an economist or a mathematician).

What makes Broadway musicals so expensive? Another talking head, Rocco Landesman, head of the Jujamcyn theater chain, noted that producing musicals involves a lot of hand labor, and there are not a lot of economies of scale. It requires skilled craftspeople not only in the writing, directing and acting but in costumes, lights, sets, sound and (more frequently than ever) special effects. And even the best, most creative people can produce stinkers. (An excellent, well-written book on the phenomenon of good people writing bad musicals is Not Since Carrie: Forty Years of Broadway Musical Flops, by Ken Mandelbaum.) All these craftspeople are unionized (as well they should be), and with fewer musicals overall being produced, there’s more financial pressure on each show to succeed.

Movie costs have skyrocketed too, and studios moan about it but they pay the price, hoping for another Titanic or Spider-Man to balance the books. But if a movie fails, there are subsidiary markets: international markets, video and DVD, television and cable, etc. If a Broadway show disappears it’s as if the earth opens up and swallows it, emitting only a faint noise that lingers in the minds of avid first-nighters.

Should we care? In his invaluable book The Season: A Candid Look at Broadway, which uses the 1967-68 Broadway season to dissect both the “show” and “business” sides of theater, William Goldman points out that Broadway is, in terms of audience size, “statistically trivial.” He quotes an NBC statistician who says that on any given Monday night there are 120 million people watching television, and that the Broadway audience that night is “maybe 12,000” — or 1/10,000th of the TV audience.

Granted, Monday is a really slow night for theater and it’s a good one for TV (this was even before Monday Night Football!), but even if you picked Saturday night — and even if you counted Off-Broadway and touring companies and regional theaters and community theaters and dinner theaters and college plays and school plays — you’re still talking about the nichest of niche markets.

But as soon-to-be-ex-Disney-chairman Michael Eisner, another talking head, pointed out, reading that 60 million people watch a TV show his company puts on is a sterile experience. But observing 1,832 people at the New Amsterdam Theatre be thrilled by The Lion King is magical.

Can Broadway musicals survive as a niche product? I guess the real question is, do they have any choice? You can moan all you want that Broadway music is not part of the popular music mainstream, but is there even a real mainstream any more? People can download whatever songs they want onto their iPod, they don’t even have to buy a whole CD. The music industry is in worse shape than the airlines.

There are some encouraging signs. Avenue Q (or, Sesame Street gets an R rating) is a clever, engaging show with a score that only gets better on repeat listens. It was the underdog in this year’s Tony Awards race but it won the top prize as Best Musical. Its creators are all in their 20s and 30s (and hopefully practice safe sex), and it has already turned a profit. And rather than touring, it’s going to that most American of vacation spots, Las Vegas, in a theater built especially for the show. Sigh. Sometimes the corn is as high as an elephant’s eye.