Well there may be a lot of windows users out there who would buy a mobile pc version over an OS X driven device, you can also point to the success or lack thereof of the Zune player as an indication. Apple has been making iPod for over 5 years while MS has only been at it for less than a year. They still have a lot to learn. A lot of people may continue to buy iPaqs or Samsungs or other phones that run Pocket PC/Windows Mobile before they buy a Zune. MS doesn't have a track record of producing hardware other than the xbox. And their track record with software is going in the wrong direction (fine by me).
As for a race, anyone who buys MS ends up on the losing side. Regardless of market share.
p.s. we all like to talk about market share and switchers, but I for one don't really want to see Apple's market share get too too large. It just opens it up for more idiots. And while not trying to be a snob, I think that Macs should be used by those who will appreciate them, like them, etc. Not everyone. I recommend Macs to friends but I unless MS kills itself and OS X becomes the only thing out there in 10 years, I am fine with a less then 20-25% niche group.