To Handle (or whoever it was that pointed out that the average height here seemed to be like 2 or 3 inches above 'normal') :
I think that the reason for this is very simple:
Tall guys are more prone to respond to a survey like this than short guys like me!
I mean, it's much 'cooler' to be able to respond "Yeah, I'm 6'7" then "Umm.. yeah, I'm 5'6"
I'm 5'11 btw. (or "almost 6' like I prefer to put it..

)