Your conclusion that gay guys have large cocks is not is not easy to support. I think that most of the pictures posted, or at least easily seen all over the Internet are gay guys. I am not anti gay in any way at all.
Straight guys do not go about showing a large cock to a photographer for a magazine. Many of us may be bi-curious but that does not mean we are almost gay. I am very embarrassed to show my cock in a public place as the public shower and changing area at the beach, because my cock will get attention. When I am there with my sons showering and changing from swimsuits, I do not want a gawking bunch of guys looking at my dick.
I have the idea that if a straight guy with a very large dick shows it a lot, he is going to be thought of as a closet gay guy. It is not acceptable for any men other than gays to show their large cocks. Because of that, most people think that gays have the largest cocks.
I do not think that is true. I have been around a lot of straight men in my life and know a lot of them have very large cocks. I have not been around all that many gay guys, but have seen many in gym showers and other places guys change and I do not see any difference is the number of really big dicks larger in either gay or straight guys. Both gays and straights seem to have a small number of really large dick guys, the same number of normal sized, and I suppose same size of very small dicks.
Hoseli