Okay some interesting info to through out there from a few bits of research I know on this. Usually the member is measured when full from the base at the top to the tip. In the case of an extreme angle, bending downward for measuring may be done. Depression into the skin is at the base to get "extra" length is not done.
Knowing that, the average white and black male are typically 6 inches. Plus or minus about 0.4 for standard deviation from previous field measurement studies. The main difference between black and white males was the flaccid state. White males as smaller when flaccid. Hence the locker room myth that black males are "bigger" when they are not on average. Anything over 7" only affects about 2% of the population just to give a general idea. I am at work and I can't exactly link the studies I remembering this data from, but a little creative google searching should find them.
The problem with America looking smaller now is our obesity. When you gain weight in the gut, it also puts on weight right at the base as well. So when taking a proper measurement it ends up smaller than it should be. So the fatter a person is then the smaller they are where it really matters. Just too much gut in the way.
But there is too much emphasis on size that makes people ashamed of being average. Especially with a certain film industry known to hire men who are actually very short in height, but a bit bigger than average down there. Then pairing them up with even shorter girls. I heard a saying about this a few times. Basically even the space shuttle would look small in the grand canyon. Meaning it's all about using artificial perspective to make things look larger than they really are.