apparently they dont in this case. just like how public school buses don't have to have carseats but private school buses do (I called to ask what the law was when my dd's private elementary school tried to refuse allowing me to put my dd's(age 4) carseat on the bus for a field trip and was told this)...sometimes there are exceptions.
We liked having a car .. but we drive the world so no need to rent. And we had a second child and stroller. But we could get to our car faster than we could get on disney transportation in most cases, get to our room faster in some cases (if the disney transport made multiple stops, and we can park much closer to our room than the bus will stop sometimes). and we get away from the noise. I hated getting on/off the buses with kids and strollers and even more hated standing on the bus with a sleeping kid balancing the folded up stroller.