I suppose, but I think back in the day people threw around terms of definition less since they were in the process of defining it. Now, as we look back on these shows and attempt to define the artform, we tend to get nostalgic about certain things, placing blame and or credit haphazardly. What about Oscar Hammerstein II and Allegro? Weill and Brecht? It's just that people expected musicals to solely entertain them for a long time (If you read the NYTimes review of the original Gypsy, available archived on their website, you'll see that the reviewer is impressed with the flashy bits of the show but disappointed by its attempts to dig deeper. Not that she/he thinks it fails to do so or anything, she/he just didn't want the play to do that. Unless I'm misreading. Of course she/he also misuses a french term).
The musical and the play are linked because they developed side by side, and you can see attempts by the musical to dig deeper all along the way, it just took a really, really long time to start getting appreciated for it. I think directors who might otherwise not be interested are more attracted to the experimental side of musical theater that involves more than just staging characters in between choreographed dances.
Also, Oklahoma came out in the early 40s. West Side Story premiered in the mid 50s. If those are the benchmarks, that's like 15 years of book theater. It really took them no time at all to start tinkering with the way things were done, which had only recently been invented by one guy who was being imitated by all the other popular songwriters who were suddenly not popular songwriters anymore. That's not much in the large scale of things.
I think it's funny how we tend to feel as if we are at the end of musical theater. I mean, really, a century or so isn't a very long time for an artform to last, especially when it only had any kind of prominence for a short number of years. It's sad to think that. That's why I get really wary of those schlocky nostalgic shows that feel like parodies of themselves. I mean, come on, the genre has to offer more than self parody. Opera still takes itself seriously, even if not many are writing for it anymore.
Blame it all on television!
yr ronin,
joey