Since that time Dean Blandino, NFL VP of Officiating, has come out and said that it was in fact a legal hit. Part of the reason it was legal is because the ball is being touched by a different player at the same time Welker is hitting Talib. The play also does not meet the requirements of unnecessary roughness since it wasn't late or out of bounds.
The fact that it was a legal hit pretty much means that he didn't break any rules. However, it doesn't take away the fact that it could be considered a dirty play or a cheap shot. In my opinion it looked like a cheap shot. Watching the play, I see Welker clearly setting his body up to make a big hit on Talib. Talib never saw it coming and the chance of him seeing it coming based on what he would be doing on the play was highly unlikely.
Now, clearly my opinion on the hit really doesn't matter to most people. However, many people are wondering why Belichick would come out with his comments. I have a couple of theories on that.
One is that he knows Welker pretty well and can read him like a book. Seeing the replay Bill might have noticed the way Welker initiated contact and knew right then something was fishing. Or maybe it was Welker's interview. When I listen to it I hear someone who appears to be covering up the truth. While I don't know Wes personally, I have heard a number of his interviews. In addition, as a former middle school teacher I'm pretty good at reading people in situations where they are being less than truthful.