Lack of demand? Pretty sure you'll find out immediately when preorders start that they're sold out.
A "sell out" is a meaningless term unless one knows how many units were available to be sold out. If company X makes 1,000 units and sells out big deal. For example the first Zune was tough to find when released. What's a Zune? Exactly.
Now Apple says for the first time ever it won't announce 1st weekend sales #s. Not hard to figure out why. Stop drinking the Kool Aid.