According to Microsoft CEO Steve Ballmer, Windows 8 represents a “rebirth” of Windows and it’s the “deepest, broadest and most impactful” version of the operating system his company has yet created.

Those are strong words from a man whose legacy may hinge upon Windows 8’s success. But Ballmer apparently isn’t afraid to use them, or to offer up bold predictions about how fast Windows 8 will find its way onto consumer devices.

As reported by AFP, the Microsoft chief believes that up to 500m users will have a Windows 8-powered device in 2013. Yes, there’s the “up to” caveat, but Ballmer isn’t shy about the implications of his prediction: Windows 8, he says, will be the “best economic opportunity” for device manufacturers and developers alike.

Given the popularity of Apple’s iOS devices and the strength of the iOS ecosystem, Ballmer’s comments, on the surface, seem a bit exaggerated, if not entirely crazy. But are they really crazy? Microsoft expects some 350m Windows 7 devices to ship this year, so the company’s ability to get its operating system into the hands of hundreds of millions of consumers in the span of a year is not out of the question.

But a meaningful chunk of the growth in Windows 7 devices is likely coming from corporate purchases, and it remains to be seen whether consumers will embrace Windows 8. Yes, parts of the Windows 8 experience look extremely compelling, but the Metro experience in Windows 8 is also vastly different than what Windows users have come to expect. That’s a big risk.

On the business side of things, Microsoft is betting that tablets based on the new operating system will play a big role in its adoption. But reports indicate that manufacturers are struggling with costs. If Windows 8 tablets can’t compete with the iPad on price, can they compete with the iPad at all? That’s a question that may not have a favorable answer for Microsoft.

The good news for Microsoft is that it is making some big, bold bets with Windows 8. Arguably, this is the right approach. The bad news? If anything, it’s that in setting expectations so high, Steve Ballmer is hammering home just how big those bets are.