I agree. But this poll makes it seem as though 6' is average - is everyone from Denmark? Probably not.
Probably the majority are from the US, Canada, UK, and Australia.
US - 5'9
Canada - 5'9
UK - 5'9-5'10
Australia - 5'9-5'10
That's my guess anyway.
Let us look at the US (where I am from) depending on where you are the height makes a huge difference. Among other white (majority being of German or English descent) people growing up there were plenty of 6' tall men. Now, I go play football with hispanics (mostly Mexican) and hardly ever see one over 5'9" with most being 5'5" roughly. So, who plays video games and frequents video game forums? The US has gotten "shorter" not because people are getting shorter than their parents, but due to immigration and birth rates in given populations. Also, fact this is english site plays big role in who comes here as well.