Exactly my point. Their animation skeletons don't match up: therefor they "just look dumb". You want character to look like that?
You could stick a model that vaguely resembles another onto the latter's skeleton: you can probably get it to rig satisfactorily (ala clones in Melee). However, having a character rigged to Mario's skeleton, but has Lucas's bat animation, you can't expect it to look anything but ridiculous. The proportion differences in the arms, fingers, legs, ect. would warp the model terribly. To make said Lucas animation work on Mario's skeleton, you'd wind up having to modify the animation so heavily, you may as well have just created a new animation.
Honestly, I do know what I'm talking about. I've worked with this sort of thing exactly (working with exsisting animations to create other characters).