They do?
Granted, anal sex does seem to have become reasonably mainstream in the straight world. It’s beyond me what the attraction is, though; the idea of it alone is just plain disgusting!
Still, it’s a free country.
Well that part is simple: it feels damn good. It’s a biological reality of the human male design, a significant proportion react favorably to such stimulus. I would personally bet on a large majority, but it’s not like I can produce a cite from a peer-reviewed medical journal. Not an easy thing to get grant money for, I’d imagine.
That said, no, it’s not a universal practice among gay males. The ick-factor is less prevalent than it is in mainstream culture, probably because simply admitting that one enjoys gay sex is already throwing out a large amount of social conditioning to begin with, but it’s still around. A few poor souls even lack whatever wiring it is that produces the deity-invoking sensations.
Harsh and masochistic? Well, that’s how the porn is always filmed I guess. Then again, in a lot of straight porn I’ve run across it looks like the woman is in a fair amount of pleasurable pain and can just barely “take it.”
That’s sex for ya. It’s mostly acting. 
Even the Family Circus has touched on this issue as well
