Linux Netbooks have a return rate that is 4x higher than XP netbooks. That simply goes beyond hard drive size, that means people saw it, purchased and decided they prefer XP over Linux.
This is also a testament to Windows marketing. When 75-85% or what-have-you have never had anything but a Windows OS, they'll see this weird interface they don't understand. Rather than learn it, they return it.
Another point, Windows machines outsell Linux machines, but no one can ever say how many are intentionally purchased to replace Windows. If I purchase one of these machines, the purchasing decision will be based on hardware, not operating system. I know what'll happen with it when it's in my house. Consequently, I'd most likely buy a Windows version, because it'll have the better hardware. If it'll run Vista, it'll scream Linux.