Bundling the 360 with Natal is more or less a price cut. Natal is being included in the price. 9 or 10 million sales in a year without a price cut in 2010. Halo:Reach also comes out in 2010, a main Halo story game which will assist 360 sales.
Xmas holiday deals would see temporary price cuts on 360 which would drive up sales. Arcade 360 could be sold without Natal for $150.