Dave: that was just kidding.
I'm trying to remember how many mobility units fit on a bus. I'm sure it's at least 2. They really strap them down well.
There was a book a bunch of years ago by the people from All Ears called Walt Disney World for People with Special Needs. They covered everything from mobility to health and I think even size. It seems to be out of print and probably out of date.
Did we mention that the boat only goes to the Magic Kingdom and all the other parks have buses from the other end? Inter-hotel buses may be more of a problem (as in no frequent or direct bus) if you book meals.
Cheers.