No one refers to costume changes as separate characters and it's ridiculous to even suggest that. No one considers Daisy to be a character in Melee, after all. Even so, it's pretty obvious that Wario's the only character with an alternate costume.i doubt very much there will be 48 separate movesets. 48 characters can be easily shoehorned in as costume changes ala warios overalls costume (lucas with a ness model anyone?)
However, I agree that we probably won't see a roster of completely unique characters, whatever the number. I have no doubt that we'll seeing at least a few clones/semi-clones.
Also, the notion that Marvel vs. Capcom 2 is not as deep a fighting game as SSBM is just stupid, I have to say.