Isn’t putting Tom Cruise and Alec Baldwin in the film of Rock of Ages a little like putting Oliver Reed and Jack Nicholson in the movie of Tommy, or Steve Martin and Frankie Howerd in the Bee Gees’ Sergeant Pepper, or Eddie Izzard in Across the Universe? It seems to be one of those bragging points for A-listers—”I’m so great, they cast me in a musical even though I can’t sing.”