Yeah...cameos don't mean a thing if a character's existence has nothing to do with Nintendo, and vice-versa.
Seriously, I'm very specific about the third-parties I think should be in Smash (stopping at Sonic and Mega Man is my personal preference), but would prefer SO many third-parties to Meat Boy. After all, the "once-you-start-moving-you-can't-stop" hypothetical play style could just as easily go to Bubbles from Clu Clu Land - an actual Nintendo character - and that would lack the gross stream of blood.