Homosexual perception in BDSM?

Speaking as a spanko, I'll admit that there is a double standard for what gender spanks what gender. It's not just about movies, but also real life situation, like spanking parties. At most spanking parties, M/f is usually the most common, with F/f coming next and F/m in third. M/m is almost nonexistant.

I think that the standard comes from an incorrect assumption that guys are fueled by their hormones, so such actions always hold a sexual connotation for us. Thus, M/m scenes are viewed as homosexual simply because it's assumed that the individuals involved have some sexual feeling from it.

Your assumption is correct, in most cases sites will focus more towards straight and lesbian action. If it's two women then it may a lesbian sex act but even if they're not lesbians it's still "hot" to most heterosexual male viewers. If it's a male and a woman it's a heterosexual sex act which they will gladly show but it's true that most companies don't do male/male scenes because it will automatically put them into the gay porn industry whether or not the scene is actually gay. So yes, your assumption is partially correct.

However, you really do have to think about where the money is and what makes the most sense. There's no question that straight men are still in the majority, and straight men will gladly look at a girl and a guy or two girls and just assume it's either straight play or lesbian play, but even a slight link to gay relations is often something they try to avoid. Furthermore, regardless of whether the scene is meant as a gay scene and regardless of whether the men are gay, most viewers will see two guys and think gay. Your assumption is correct that the industry reinforces theses as ideas because the end fact is that's already what their viewers believe and they have to go along with their viewer if they want to make a profit.

I think you need to look at the target audience. Who exactly is more likely to view man-on-man BDSM sites? Gay men?

I have seen male/male BDSM sites on the web without the gay undertones to them, they are just hard to find. They seem to be marketed to women and "gay/bi" men with a "straight" male fetish. Like everything that has to do with porn its on the net you just have to have the want to find it.