As long as your biggest market is people who want it done for them, and as long as it's affordable, the OS will continue to drop into their hands. The price increase for the various iterations of Vista show that Microsoft is at least aware of Windows' continuing strength.
If you want OSS to blossom, it has got to become sexy and work with much less nerd/geek presence. Symbian happens to power smart phones, but it's not sexy either. It can't spoil you in that "mainstream-moves-the-most-water" way, like Windows can.