On some level, I agree with Dyack in that previews can be a bugger for everyone involved. I just don't buy him making this argument, seeing as how he himself, and I doubt this was all dictated by a contract, kept the flow of hype going pretty strong for a while there. And as said, the goalposts have moved, and I'm not sure why people are expected to simply forget the early words on the game.
And if he wants to be taken seriously, he really should be lashing out at those who then, without any first hand experience of their own, largely repeat the good things that Dyack has said about the game. If you really want to make a case against pre-release criticism, then make it count in both directions. But that won't happen, because the dude is only human. He doesn't like his games being ripped to shreds, which is understandable. But his insistence that he is somehow arguing from a higher position, that's what makes it so god damn easy to fall in line with the haters.