Well lets look at something. We know a few things about the development process...
1) Some characters are more developed than others (Megaman/FitTrainer are lacking a few animations and frames, even for their respective characters)
2) This game was probably built straight off of the brawl engine.
Mario is seen with beautiful animations, moves that flow nicely and most importantly, a more complete look. He is also the character seen with the altered ledge mechanics. On the other hand, FitTrainer is a bit more choppy, with many animations not done and once again, does not look complete. Her ledge mechanics seem exactly like it was in brawl.
Another thing we know from brawl hacking is that ledge grab range and all that fun stuff is done on a per-character basis. If the engine is the same as before, it's really possible that the FitTrainer we see in the videos is a 'rush to get her in the E3 lineup' character, while Mario was probably the first character fine-tuned due to his neutral, flagship nature. It's pretty safe to assume that Mario is more complete than the other characters we have seen gameplay of, and that we should be using him for our benchmark for everything.