The "sex" that tends to get discussed on these boards is actually very middle of the road. There are lots of "alternative" hobby-type things which go on that you rarely hear about ( Transexuals, B&D/S&M, GS, etc. ). Some of it doesn't get discussed because the guys who are seriously into it have their own boards and other issues. But the other part to why it doesn't get discussed is becvause guys don't want to be made fun of, shunned, etc. I'd be willing to bet that there are plenty of hobbyists who do see either "alternative" providers ( dungeons, etc. ), transexuals, or ask for "alternative"services ( GS, etc. ) from the "regular" provides who they do see.
There are at least 100 transexuals who make "a living" ( i.e. are not part-timers ) in NYC, which means there are probably thousands of guys who see them at least "once in a while". Of course, when anyone mentions it on one of the boards, you see all sorts of comments, so they clam back up again.