I don't know what Natal costs to produce, but I do know it needs to be pretty affordable unless MS just wants to target early adopters and build for their next console.
If it's too expensive (and I guess MS cutting the CPU implies it was too expensive in terms of the original build) then it could really struggle to take off.
I guess MS might need to consider selling at cost or even a loss if they want to secure high demand.
Try to be reasonable... its easier than you think...