Why are chuck norris jokes so funny?

I see them all over the place and my friends are always laughing at them, but why are they funny? Like what makes him so great in the jokes?
I'm probably an idiot for not knowing, but oh well. And I hope you see what I'm asking in this question.

because its normally true, or the fact that he is so for-rel in things, it becomes true>.<

I don't know but some are so random that its amusing, like "How much wood would a woodchuck wood if a woodchuck could Chuck Norris" it doesn't make sense but hey...

they are pretty funny, Mr. T and Chuck Norris walk into a bar, then the place just explodes. why? Because that level of awsomeness has never been in one place at the same time, lol I don't know, there just so supid there funny.