That's the bad news... the good news is that you can find unlocked or unlockable Android devices that are way more mainstream than any of the Windows and OS X competitors ever managed to be. Yes, certain apps that require DRM won't work but on the whole you're way, way more mainstream with a rooted Android phone than a Linux desktop. And Android is making the OS a commodity because if you don't need to be on the bleeding edge you can always download the last released Android version for free, even cheap Chinese clone makers. There is no way Apple will be the ones supplying most of the world with cheap smartphones unless they completely change their business model.
Tablets are a bit earlier in the market development but there's no reason to think it'll be any different, Apple will skim the top with the iPad but eventually Android will be the Nokia (pre-suicide) of cheap tablets to supply the world. Globally most people simply can't afford an iPad and they never will, but they'll take whatever cheap hardware someone can put a $0 version of Android on. I guess it's not the future RMS or Canonical wanted, but Apache is a proper Open Source license and the kernel itself is GNU/free. And there's now plenty of applications and developers for that open source system, building inertia that will rival what Windows has for desktop applications. I think your glass is very much so half empty if you think this is a "Phyrric victory".