The battle for number two is about to get serious.

A quick look through the halls of Mobile World Congress reveals an endless number of iPads, quite a few Android tablets, and almost no touchscreen Windows PCs. But Microsoft is here in Barcelona promising that balance will change dramatically by next year — the company just released Windows 8 Consumer Preview, a beta version of a radically new version of Windows built with tablets specifically in mind. And while Windows 8 has a long way to go before it can challenge the iPad, it feels almost inevitable that Microsoft will quickly succeed where Android tablets have thus far failed — especially because Microsoft is aggressively courting developers to write apps for its new Metro interface.

Google isn't sitting still, of course: Android head Andy Rubin promised this week that Google would "double down" in the tablet space this year and "make sure we're winning." But it's not clear how he plans to do that: although Android has rocketed to dominant marketshare in smartphones, it has thus far flopped on tablets, and Samsung admitted this week that it's "not doing very well in the tablet market." That's not very encouraging: according to Rubin, Samsung tablets are the most popular of the 12 million Android tablets sold thus far.

Perhaps more importantly, Google doesn't seem to feel any pressure to increase the quality or quantity of Android tablet apps, which have lagged far behind their iPad counterparts. Rubin told reporters this week that he "can't force someone to write a tablet app," but that he's hopeful developers "put in the muscle" to make their Android phone apps work better on larger screens. Until Google articulates a clear strategy to make Android relevant on tablets, that doesn't seem likely to happen.

Microsoft's approach is quite the opposite: it's heavily stacking the deck in favor of its new touch-friendly Metro interface. Developers can't sell non-Metro apps through the Windows Store, and non-Metro apps won't run on the new ARM-based machines at all. That's a big deal; Microsoft isn't necessarily shy about the fact that Metro and ARM are the future of the platform, and it spent a good portion of its Windows 8 Consumer Preview release event yesterday highlighting Metro apps from developers large and small. "We have the best app economics out there," said Microsoft's Antoine Leblonde. Google makes no such promises. By all appearances, Google is simply hoping developers create great Android tablet apps while Microsoft is pushing them towards Metro and providing significant rewards to those who get there first.

What's more, Windows 8 may soon be a major force in the tablet market simply because it's Windows. Windows 7 was the fastest-selling OS in history, and if Windows 8 approaches those numbers, the market for Metro apps will simply be too big to ignore — what Microsoft's Leblonde called "unprecedented reach" for developers. A tablet market dominated by the iPad and Windows 8 may simply not leave any room for a third platform like Android to succeed; consider that Microsoft itself hasn't made any headway with Windows Phone 7 in a smartphone market dominated by Android and the iPhone. While Google's Rubin was candid about the challenge of attracting developers to a platform with a small marketshare, saying that app developers were being "frugal," Microsoft's Steven Sinofsky was far more bullish, calling Metro a "huge opportunity for developers."

But the biggest challenge for both companies remains Apple, which continues to relentlessly improve the iPad and iOS — earlier this week the company neatly upstaged an entire day of Mobile World Congress by sending out press invites to its March 7th iPad 3 event. Until either Microsoft or Google can demonstrate why their products are compelling alternatives to Apple's tablet in a way that resonates with average consumers, the fight for second place might continue to be a fight for not much at all.