No way to know this of course but I think they are playing this a little as it goes. That is the way we ramp up users when we roll out new apps, granted our concurrency is not even close to being in the same league as BW's but it is a generally accentped way to roll out apps and see how the servers respond.
Don't you really think they are doing everything they can to let as many people in as soon as possible? I mean for what reason on earth would they want to delay it?