Wow, you've never played football in your life have you. It can be like that in an y game from an AFC championship to a good nice competitive high school game in Ohio or Texas. That's just a way to get into the head of the opponent and, like the article says, its usually employed by offensive linemen (who rarely get called). The pats d-line just pays'em back in the same fashion. Seymour was successful too judging from Harwick's whining afterwards. The guy can apparently dish it out (see his quote before the Titans game "we're dirty too") but can't take it himself.
You think a shove, hip-check, or slap is dirty? That won't really hurt someone. It'll just get them to lose their cool but it certainly won't result in career threatening injury. Dirty is diving at somebody's knees, breaking an arm or twisting a leg in the pile, or taking somebody's head off with an unseen facemask pull. Dirty is the Broncos o-line, Hines Ward, the Titans, or even (as much as it pains me to say it) evil Chargers Rodney (who still ocassionally shows up in place of good NE Rodney).