It doesn't state anywhere that the are flying, just that they can fly, and Kaos is in more of a hover than straight up flying most of the time.
I mean, if something is coming at them, why wouldn't they fly out of the way? >_>
Kaos can teleport, too, so...
According to Kan, if you are being "very generous" the shell can start 10 yards away. At 60mph it would take a third of a second to reach and hit everyone on that platform. They dont have enough time.
I know it's pointless to argue at this point because no one seems to care about actually looking at the facts but I am not going to give up just because of that.
This argument has been done before, if it makes you feel better, by Scare in his very first match with bowser. In a Wrestling ring. ---