Demand is obviously not low...the site got shut down last night. I think its either 1 of 2 things:
What we experienced was a massive fanboy rush (in which case there are a LOT more fanboys than I had thought), and they all finally got through and the waves of regular folk haven't gotten up yet or:
Last night did see many people preordering, but they all got fed up and went to bed, and aren't awake to start hammering it again yet
or, like you said, apple did something and got their site to a point where it can handle it