Other guitarists will point out mistakes of another player, because I think we have some pride in what we do. I do it too. I can't speak for anyone else but myself, but I don't think it's done to curse the other guy. Just the fact that I can notice that, doesn't mean I'm saying, "haha, you messed up, so your a horrible player". I could play the same song and someone else will notice where I would mess up somehow. It's an endless cycle like evil sheep said, it's going to get noticed (criticized) by someone because your going to make mistakes.
The guys you were talking about are still on rhythm, even if it's not exactly precise. Their is just alot of feeling in it, and if your playing by feeling; there is going to be some kind of rhythm to it if your on with the drumbeat behind it. Any musician can appreciate feeling and emotion in music.
"My whole life is a dark room...ONE BIG DARK ROOM" - a.f.i.