That was an idiotic comment but for the small amount of his show that I've seen I like him. He's entertaining and critical of both sides from what I've seen of him.
I like him too but that doesn't mean that I agree with everthing he says.
Maher's point - he saw planes hit the buildings so of course that's all he needs to know (granted I've paraphrased)
That's a pretty simplistic and ill-informed conclusion (I'll spare the arguments - they've been hashed out here ad nauseum)
I guess the signifcance is that he's on the left
Would it do any good to trot out all the people on the right who have serious questions about the popular narrative about 9-11?