I've been wondering this as well, Kekken.

Bigger karts definitely DO impact gameplay in Mario Kart DS for exactly the reasons you indicate-- in Wipeout, this could be an especially big deal because of the importance of tight cornering. In principle, it would seem that a "thinner" ship could take tighter corners.

I'll be curious to see what others think-- and also to see if the developers jump on and answer this question.