This is a good article by Gamespot about the Xbox 360 inventories. Microsoft "aware" of 360 shortages - News at GameSpot.
Is it possible that Microsoft that Microsoft wanted to run out of product very quickly. Sometimes it is a good idea to have incredibly high demand that can be accentuated by low supply. Or, perhaps Microsoft has not fully put the device into production in anticipation of some or many of the problems being discovered in the market place.