Just because Glee is a phenomenon and High School Musical made money doesn't mean perfectly clever non-musical sitcoms can go throwing terrible production numbers into the mix. It isn't genre experimentation, it's just annoying. Also, High School Musical was terrible, so no one should use those songs as a role model.
I completely, completely agree. Musical numbers in sitcoms work when they're used to extremely specific ends. In Buffy, the music came from a one-time demon appearance, and with the goal of getting the characters to speak aloud things they'd been concealing. The concept was cute, but it was also a major tool to drive a bunch of plot lines forward. What works in Glee is not just that it's a bunch of kids singing all the time, but that their reinterpretations of songs we know extremely well are consistently very good, and challenge our conceptions of what those songs should be. Since hearing this, I have not been able to cope with the fact that "Halo" is not a fast number:
In a weird way, I think the ultimate expression of this was less any one of the million sitcoms that have gone here, and more this weekend's Academy Awards. Neil Patrick Harris's opening musical number was cute, rather that sterling. But worse, it was a representation of the producers' inability to stick with a consistent concept, and perhaps of Adam Shankman's inability to let a fad that allows him to use his musical theater skills, pass him by. Musical numbers in sitcoms work when they're surprising. The fact that today they're expected is what's killing them.