Well, to be fair, Bones doesn't know that. His line of reasoning runs as follows: 1) People on the roof shooting each other means they have a precarious grip, 2) Emergency brakes are quick because of the word "emergency", 3) 1 and 2 together don't sound like a good idea.
Besides, we're bringing physics into a discussion on a d20 game...Catgirls are dying left, right, and center here.
And yeah, good thing we've got a doctor around to patch everyone up...