A lot of the online gay porn market consumers are people who live in conservative states.
Check out the top 10 states searching for "gay porn" and compare that to the link below that.
http://www.google.com/insights/searc...mpt=geo&geo=US
http://en.wikipedia.org/wiki/File:PurpleNation.PNG
People suppressed by the "social norm" in their vicinity. Their only outlet may be adult material online.
Why does gay and tranny porn convert better than the other major niches? I don't think it's a lack of content.