Once when I was looking at helmets on the internet I ran across a helmet that was approved in Europe but not in the US because it had less than a perfectly smooth outer shell. Apparently at that point time the US rules were rather strict on the subject. If you are really interested I suppose you could try to track down the regulations on bike helmets. For me, I have just logically concluded that I want to stay away from the problem even if it is ok with government. Velcro though seems like a good option.

Wayne