The problem they have is they can only afford, one, maybe two more big flops, or even medium flops, before they finally loose their strangle hold on the market.
Business users aren't going anywhere. They've got too much invested in Windows to jump ship on it. They'll likely do the same thing they did with Vista, just stay with their current system and wait for Microsoft to pull it's head out of its ass. The whims of business dictate to Microsoft what they're going to do. If the business world looks at a version of Windows and goes, "NOPE!" then you can be damn sure Microsoft is going to react and try to fix it for them.
Home users are heavily influenced by what they know and what they use at the office. The average user wants nothing to do with Linux and likely never will. Mac's may make up some ground but people are not unlike businesses in that they are heavily invested in Windows and aren't going to jump ship easily.
Microsoft seems to have sensed a changing market since Win 7 came out with the rise of tablets and the so-called "post-PC" world. As others have said, Microsoft has no foothold in these new markets at the moment: this is their gamble at remaining relevant in the changing face of computing.
Ugh, this "post-PC" bullshit. No one is changing in their desktops for tablets any time soon. The same way that the laptop did not rid the world of desktops, tablets will not do it either. They will find a place in the continum of computing the same as other devices are. The desktop isn't going anywhere and neither is Microsoft's share of that market. It's an attempt to have their "thing" they can crow about to differentiate themselves from others in the market for smartphones and tablets. Apple has the hipsters and people who don't like computers. Android has the people who hate Apple and/or aren't terrified of the idea of tinkering with their stuff. Microsoft is going to try and market themselves as having a completely integrated range of offerings that their tablets work like your desktop which works like your phone which is a tiny tablet.
I'm honestly not convinced that anyone cares. I know I don't. I don't really need the same OS on every device I own. My droid is pretty intuitive, Apple's even more so. There's no trouble at all keeping the OS's straight. As for sharing data across platforms I'm not really feeling it. With Amazon MP3 I've got all my music available on my phone, my tablet, and my PC. I work on documents across platforms with Google Docs. I still use sync cables for things like pictures but anything that important goes into my cloud drive so I can get it anywhere. So... yay for integrated OS's? I think they'd be better off trying to differentiate the Surface as a productivity tool first and a toy second. Really push the Surface as a laptop replacement instead of what their current commercial does which is, "Pretty colors and dubstep!" Then use that as a jumping off point instead of pissing off the home PC market and making it highly unlikely their business customers will want it either.