Solis24: With the facilitation of information exchange through internet, chat, and just a general relaxing of people's attitude towards sex, it would be logical that you would hear about larger penises more often. You're in contact with many more sources of information and are hence more susceptible to hear/read something about it so it would be easy to think that there's more. Much in the same way, because more and more gay guys are coming out, some people tend to think that there are many more gays now than some 50 years ago but maybe it's just because it's less of a big deal now than it used to be so you hear more about it.
On a non-sexual note, some people even claim that the end of the world is near just because "more and more disasters are occuring". Are there really more or have the media gotten a lot more efficient at relaying information, causing us to be aware of more disasters than we normally would? I choose the latter...
Back to the original topic, there is of course the hypothesis that all the hormone-laden food we eat has affected us in a way, the younger generation more visibly so. A lot of the meat we eat in North America has been boosted with hormones to make the animals grow more meat, just think of chicken breasts. These hormones aren't necessarily broken down in the cooking process and may affect our bodies as a consequence, which could be a reason as to why teens seem to physically mature more quickly than a few decades ago. While I'm still skeptical about this one, I can't really dismiss it either.
Ok, bottom line, I think I can think, but I don't know for sure