You might find a little thing called bribery involved here.

Microsoft: "Can you install WinXP on these here netbooks?"

Manufacturer: "Of course, but we have to pay for Windows licences and then the product becomes more expensive. Linux is free..."

Microsoft: "What if we give you WinXP?"

Manufacturer: "We still have to put better hardware in which makes it more expensive"

Microsoft: "What if we discount your licences on your other products more than we already do to make it cheaper?"

Manufacturer: "That might work..."