Are you referring to my comment about buses or vans?
Buses, I'm okay with. Statistically they are safer than cars, but a large part of that is because they get into fewer crashes, for all the reasons Bren's Mom listed. I still worry a little more about them at highway speed, but not enough to keep my kid off a bus.
15-passenger vans, on the other hand, are a well-known rollover hazard, especially when the drivers are not very experienced with that particular vehicle (you can drive a car for 20 years but it will not necessarily prepare you well to drive a 15-passenger van). You can read more here:
http://www.nhtsa.gov/cars/problems/studies/15PassVans/15-PassengerVanConsumerPiece.pdf
http://www.citizen.org/autosafety/passengervan/ (several links at the bottom for more info)