Heh. I had exactly the same response: it didn't sound like Chomsky to me. I even commented to that effect, but then had second thoughts and deleted it. It wouldn't be unnatural to use a different voice in a casual email than in a published article. Also, some of the things in there do sound distinctively like Chomsky (e.g. the second last paragraph).
I searched around for more on Chomsky and postmodernism and came up with http://archive.zcommunications.org/chomchatarch.htm, which includes quotes from the OP. So it seems it's at least partially authentic.
As for whether he would have had time, that's easy. It's already impossible to explain how he has time to do what he does.
Edit: I also ran across a clip of Chomsky's discussion with Foucault on Dutch TV from the early 70s (http://www.youtube.com/watch?v=kawGakdNoT0), which was fun to take a look at. Can you imagine anything more un-TV-like? The very length of their sentences is unthinkable - I was going to say "nowadays" but I bet it was unthinkable on TV even then.
I read the whole thing, and I thought it had Chomsky's voice. I've read a few of his books, and listened to him speak (not in person).
I agree, it reads like he talks. Could it be a transcript?
After reading only a few lines of this article it struck me as inconsistent in tone from other speeches and writings of Chomsky. So I would first like to get Chomsky's response on whether he authored this. Considering how many interviews and public speeches Chomsky gives, I find it hard to imagine him having the time to debate his ideas on Internet bulletin boards. Unless he was experimenting with the format back in 1995.