If you sell an ARM powered netbook that means no windows. So you can wave goodbye to being able to use OEM copies of windows on any other products that you make.
So anyone like Asus or Acer that have a PC business and launch a non-windows netbook soon learn the error of their ways.
They can sell one line of Windows-proof highly capable, futuristic computers while keeping and developing their legacy-ish, kludgy, virus-infested, Windows-bundled, 8080-descendant-based inefficient lines.
Of course, Microsoft will probably find a way to increase their OEM pricing, specially if the Windows-proof line ends up making a dent on the Windows-bundled lines. And they don't even need to increase, say, Asus's licensing prices. All they have to do is to lower Acer's.
MSFT tend not to increase pricing they tend to say - ship even one computer without Windows and you wont be buying OEM Windows for any of your other machines.
They've gotten in rather a lot of trouble for doing that in the past. Do you have any evidence that they have been doing it since the emergence of the netbook market?
So anyone like Asus or Acer that have a PC business and launch a non-windows netbook soon learn the error of their ways.