How so? I can think of several projects (especially hardware) that they abandoned after the first version. Granted, they gave the Zune a fair shake (though I don't think the iPod had much to be scared of). SPOT, too, considering that smart phones were starting to get useful about a year after SPOT's release.
But as a counter example, I know of one unreleased hardware product they're working on right now that stands little chance of going beyond V1 due to (without inappropriately saying too much) a lack of commitment on MSFT's part. Could be that in this case they're not "determined to win", but I'm not in a position to know how determined they are.