At the risk of perhaps angering the Linux community here (I work on a Linux box too), may I suggest that's where Windows 8/WP7 is going? And at further risk of anger, I will suggest that Android has reached its peak.
Evidence for point 1: Windows has such a large base of "desktop" applications with a larger base of active developers. Not only that, the majority of the world uses their standards for word processing, spreadsheets, presentations, etc. Honestly, OpenOffice and GoogleDocs are both still horrid. Horrid. Compared to Word 2010 on both Windows computers and OSX-based computers. Guess what? Most of the world, including us techies, still need to present, write documentation, yadda yadda. Perhaps when/if someone else develops an open/Ubuntu/RedHat/etc office suite that can actually match MS Office in ease of use and in reliability, then I'll change my mind.
Evidence for point 2: Android has grown quickly in the past three years because (in my opinion) of personalization, novelty, hardware, and free angry birds (maybe not). Android being "open" really...doesn't make a big deal to your average consumer (again, this is my opinion based on what I've seen). The big issue that's splitting through the three major draws for Android-based devices is massive fragmentation. On the device side, there are so many Android phones that ALL LOOK THE SAME (but are slightly different), that come out every other week, the novelty of owning "THE NEWEST ANDROID PHONE" dies out every other week. The fragmentation between devices is also massively confusing to the average consumer. Does the consumer want...the Galaxy S II...the Galaxy Nexus Prime...or the Nexus S? And by the way, what's the difference between all six (there are four flavors of the Galaxy S II) of these phones?? Software fragmentation is also leading to a fairly horrid user experience as developers have to develop for 2.3, 3.2, and 4.0.4. Never-mind that the UI actions for each of these OSes are very distinct and different, the UI LOOKS COMPLETELY DIFFERENT.
I don't know. I'm using a RAZR (first on 2.3 and now on 4.0.4) and I'm still not satisfied with Android. This is coming from one of the first adopters of the G1 (which I still have, and it still functions). I am eagerly waiting for the next generation (after the 900) of Windows phones.
(Wow, this didn't mean to turn into a rant...but hum.)