My understanding was that each branch of the major chains got 30 units each, with notice that that was it for the Christmas season. I also understand that Microsoft was in such a rush to get XBOX 360 out this season before Playstation 3 is released next year, that there are design flaws in the unit--most notably, if you play the game for 4 consecutive hours (and what kid doesn't), the game heats up to such a point that it locks up until you cut the power and the unit cools down.
Another major design flaw -- in the horizontal position the 360 scratches discs. It can also happen in the vertical position if the 360 has spent any time resting horizontally. Also, if the box is tapped or nudged in the vertical position, the discs can be damaged. Microsoft does have a fix for it.
They rushed the box to market and they are artificially creating scarcity.