I rather wait long and get a proper "product", than get it soon/fast and it has a lot of bugs.
And even if those bugs are of the smallest kind, the community will complain about them!
It will (probably) never be free of bugs.. Unless someone works over-time and focuses on even the trivial ones.
It is impossible too, to predict what kind of bug/exploits players will find because they are able to invent just anything, something that nobody thought of yet!
And then again, after the content is done, testing it in so many combinations with the already released content...
It is a complex process, extremely. Going from top of the ladder to the bottom of it.
And sadly, the community is not always supportive =(
I also want Naxxramas, now, already, today! But, I do understand why it is not here just yet.
If content is announced, it is whining about "why isn't it here yet?", when it is released it is whining about "why are there bugs x or y?" or "x and y are too strong", it is _never_ good enough.
Not everyone will be happy, I guess.. But, it is about making the majority happy
No people are annoyed because blizz says something and then dont hold onto it, but w/e cant change it anyways its done when its done.