I've learned to ignore numbers when it comes to this site (or worse, in real life, especially coming out of guys' mouths). Every girl has had a boyfriend or husband that was 10" long. Like someone previously said, 10" is longer than the notoriously huge pornstars who are only famous due to the mind-boggling size of their penis.
I think lots of girls here just unintentionally add in ballsack inches with the length. From a girls' point of view, it looks like a continuation of the shaft, which is why they include it. An 8" penis is exactly what girls would call 10" because of this. You get a very different measurement measuring from the top. This is why the average is 5 1/2", which seems kinda small if looked at on a ruler, but this is because it's assumed that you're measuring from the top. From a different point of view, it does not look 5 1/2", it looks about an inch bigger.
Oh yeah, and guys also lie. A lot. This isn't news though, right? Schwing!