Linux started the Netbook market. Windows is a late comer. However, as I always said, Microsoft knows a threat when it sees one and have enough muscles and inertial to negate its disadvantages as a late comer.
To tell the truth, I do not trust any sales/statistics figures coming out from the Netbook market. For one thing, the segment is too new. It has completed its initial phase, the phase that decides whether it is a dude, just another computer or full of promises. I think it is safe to say it proven itself to be full of promises. It is just ripe for the next stage, where you see a lot of innovation and competition for that segment. What will emerge out of that phase is anyone’s guess.
Having said I do not trust sales figure, I am going to point you to an article on Network World that claims Microsoft rules Netbooks which quoted Microsoft as having 90% of the market. I still do not trust the statistics, but will agree that Microsoft is a rock-solid competitor in that market segment. In my opinion, if this means in best case scenario Microsoft only manages a 90% market share means the market is still very competitive. I would had expected Microsoft to sweep the floor (95%+) by now. 10% is enough to gather sufficient momentum to ensure innovation do happen. As the article itself points out, a lot of IT industry heavyweight has their crosshair set on that market, meaning if I were Microsoft, I will not confortable with a 90% market share at this stage.