In example two of plot being forced to play to the musical theme, Finn (Cory Monteith) jumps into bed with the lovely Santana (Naya Rivera), who suddenly grows an interest in him via very weak reasoning. But he feels nothing after the sex, and she doesn't seem to have any further interest in him. Finn is a bit more moral than to just have casual relations. Because Santana is smoking hot, and she is openly propositioning him, perhaps hormones can be to blame for his actions. But then those same hormones should lead him to feel the carnal act is fantastic, not a let down. You can't have it both ways, Glee. Pick one.
Honestly, Finn probably only gets into bed with Santana for vocal fill out in "Like a Virgin," and perhaps so one couple in the song can actually do the deed. After all, Rachel (Lea Michele) won't put out to Jesse (Jonathan Groff) quite so soon, and we all know that Emma (Jayma Mays) has a ways to go before she can give herself over to messy, fleshy behaviors. The other two pairs are fated to never do the nasty from the beginning.
"4 Minutes," by contrast, actually feels fitting. After all, Mercedes and Kurt are playing second fiddle to others in the group, and Jesse joining the New Directions will only make that worse. They help out Sue, so she doesn't hate them as much, and their addition to the Cheerios will only boost her group. Thus, with their singing talent and "The Power of Madonna," they make a really great addition. It's all much better than the earlier "Ray of Light" cheerleader number.
The other songs in the episode, "Open Your Heart / Borderline" and "Like a Prayer" are just big, splashy production numbers put in place purely for fun. They work because they aren't trying to be anything more than they are, and Madonna makes great music. Even "What It Feels Like For a Girl" is sweet and touching, if a bit unneeded. Let me explain,
Honestly, the entire concept that the girls of the New Directions are being torn down and need empowerment is a load of hogwash. Glee is more gender fair than almost any other series on television. The girls' "Express Yourself" is fun, but they are not crying out to be recognized before now. Sure, Tina (Jenna Ushkowitz) might need a little confidence booster. And Puck (Mark Salling) might not care about the girls' feelings as much as he ought to. But is this really a widespread problem? I surely can't see Mercedes allowing herself to be pushed around, or she'd do another round of window busting. Rachel wins Jesse a stuffed Care Bear. Finn is going to do whatever he can to make the girl he cares about happy. The guys act a bit more like tools in this episode, but not enough to justify the girls' outrage, especially because it's not their normally shown behavior. So major fail in an essential element.