Yeah, at least Roy wasn't quite as big a jerk to Pam in the American version.

I figured it was simply a play on the cliche of how nice women always go for horrible men. Lack of self-esteem and whatnot, believing that this is what they deserve. The only time I didn't feel sorry for her was during series two, when Tim got a girlfriend. I kept thinking "quit acting jealous, you could have had a shot with him, and you effed up". Then I remembered it was a TV show, and laughed.
Also, we don't know much about their history, so at one point he may have been a really great guy, but working a blue collar job around a bunch of jerks might have made him a jerk as well. But I doubt it.