Thanks for your excellent post, sykray -- it really helps put things in perspective. I've read that reputable studies have put the average at 5.1", but had not seen all the additional statistics that you cite.
What I find most interesting in relating these statistics to the original query on percentiles is that apparently 6.2" is at the 83rd percentile, and any guy above 7.5" or so (a size that some here don't even consider "hung"!) is in the 99th percentile.
One of the really unfortunate (and very widespread) penis size myths out there is that average is 6", a distortion that causes lots of guys to underestimate themselves. Think of all the guys who visit this site and call themselves "average" at 6" (~80th percentile) ... or who are 7" (~95th percentile) and doubt that they are well-endowed.
Steve