Market research is a very interesting thing. Also, they have internal metrics, and... well, when you unsubscribe they do ask you why you left. :P
As for the WoD launch fiasco, just look back to any launch they've had in the past six years. None of them has been seamless, because it makes no sense to prepare yourself for a burst of 100,000 concurrent players when your server is only going to hold 20,000 players at peak times. Once the amount of people trying to play the game stabilizes, you're left with an enormous amount of computing power that's effectively wasted. So they deliberately take the PR hit during the first few days of an expansion, because the problem solves itself with time.
It's like putting six front doors in your house that allow for 12 people to go through at once, when 99,99% of the time only one of the doors is going to be used. Sure, you could do it, but then you'd have a lot of expensive doors that never get used, and you still have to pay for maintenance for them.