Peter Moore says they're simply being conservative.
In every way, Xbox 360 had outperformed the original Xbox, but despite having a year-long lead on the competition, the machine hasn't exactly sold in gangbusters, as many were predicting. Consequently, Microsoft has quietly scaled back its shipment predictions for June. They had previously aimed for between 13 and 15 million hardware units, whereas now it's simply 12 million, says The Mercury News.
Microsoft exec. Peter Moore, however, says it's the result of the company being conservative, in light of inventory build up at retailers, and to move those consoles would require heavier marketing, which would require more money, and, for now, Moore seems content not taking that step quite yet.