Hank Pym smacked Janet back in the 80's or something in the 616 universe. In mitigation, he was in the middle of the same psychotic episode that generated Ultron, and he didn't go all lunatic bug spray on her, but that's where that comes from. It's also managed to be obnoxiously character defining over the years, in that no one ever lets him forget it, despite, say, that time Reed smacked Sue with nowhere near as good a reason and no one cares at all.
Per Brian Cronin -- who sites both writer Jim Shooter and artist Bob Hall -- it was also
not in the script. As Shooter wrote it, Hank was supposed to throw up his hands in frustration and accidentally strike her; per Hall, he tried drawing the sequence multiple times and just couldn't make it work and decided to, in his words, "do Marvel Action" and make him haul off and smack her.
Or that time Peter backhanded Mary-Jane while she was pregnant.
Which, I'll admit, was during the Clone Saga.
Which I think is why all the fans pretty much immediately decided It Didn't Happen and have basically ignored it. (And of course now, post-Brand New Day, it actually DIDN'T happen, canonically.)
I think the major difference is that people generally liked Peter Parker and hated the Clone Saga. Collective shrug; fandom decides It Doesn't Count.
Whereas, in a lot of people's minds, hitting Jan was the most interesting thing Hank Pym had ever done, and so it became permanently attached to his character, like Iron Man's alcoholism or any number of other horrible albatrosses that various people put around heroes' necks in the 1980's.
Bal's right -- Hank was "the wife-beater" in fandom's minds years before Millar got ahold of him. It was even a major element both of Busiek's main Avengers run (with Perez on art, for most of it) and the Avengers Forever mini that he co-wrote with Roger Stern (drawn by Carlos Pacheco).
I actually thought Millar's creepy take was the highlight of Ultimates -- just as I think Marvel should have let him and Hitch kill off Stark and Fury at the end of their run like they planned. I think that kind of stuff is exactly the sort of thing that the Ultimate Universe should do -- really jarring stuff that violates the hell out of the kind of status quo that the main MU has built up over the past 50 years.
In practice, of course, the MU's just gotten more like the Ultimate U and vice-versa, to the point where it doesn't really make much sense to have both anymore, and we're once again on the verge of a Big Event which is rumored to be the end of the Ultimate Universe.
(Bears adding, though, that for all the influence The Ultimates had on the Avengers and its related films, most of that influence is from Hitch, not Millar. Scott Kurtz's obnoxious little "Which looks more like the Avengers you saw in the movie?" post has a point -- but the point it ignores is, which characters ACT more like the Avengers you saw in the movie? Movie Captain America may dress like Ultimate Captain America, but his behavior unmistakably draws from Simon, Kirby, Lee, Brubaker -- but not Millar. Not for a second.)
