Windows 8 Tablet versions are still Windows 8, although many tablets will use the ARM processor instead of something that understands Windows-Intel predecessor CPU version instructions. What does this mean? Barring a processor emulator, you won't be able to copy your old Windows apps onto an ARM tablet and make them work. If you buy a tablet and want to run your Office license, it's a no-go. Games? I don't think so, unless they're ported to ARM. Like those utilities? Nope. Plug-ins for your browser? IE 10 won’t support them on any platform.
Do you care?
The answer is probably you probably won't. The answer is complex and competitive, but to summarize, system designers don't view tablets as PCs or as upgrade paths from PCs. Yes, things will look like browsers and your old favorite applications, but that's merely a mirage. Tablets are a convenient way of saying that backwards compatibility is unlikely, although a few things will fit and work.
Tablets are designed to be content and entertainment consumption devices. They have hard drives mostly under 100GB and for a good reason: space and power consumption. Your old stuff's not going to fit. Plus, think of it this way: it's a whole new device to fill up with videos, your music, all of those cute photos you're going to take with your tablet, and a host of new applications. This is because most of your old applications aren't going to work -- especially on ARM-based tablets.
Apple used its iOS, rather than its MacOS, to fuel the ARM-based iPad 2, and for good reason: battery life and stricture. Imagine: you buy a 16GB tablet only to find that your payload of every element of Microsoft Office, plus your music collection fills the tablet to its very brim. No more room. You'd be happy with that, right?
There are lots of reasons to leave your old stuff behind. To keep your XP programs on an ARM tablet, you'd need a processor emulator, like the Transitive software app called Rosetta that Apple used to translate PPC to Intel instructions. It's unlikely that it would be perfect. You like perfection, right?
Imagine that your XP machine was also sodden with various anti-virus/anti-malware applications that ssslloowweed your machine down. You like slow, right?
The XP apps that you'd use on your tablet may or may not fit within the tablet's screen geometry. They were optimized to work on a machine having a big fat battery or better still, a PC of a decade ago when XP first arrived. Apps drink power at sometimes furious rates and weren't optimized with power consumption in mind, rather, to be fast and beautiful. Tablets can do both, but it's a different formula that gets there.
Microsoft is said to be strongly active in vetting Windows 8 apps, which will be important from a credibility standpoint -- Google and Android suffer from an inactive application security vetting. Importantly, Microsoft gets to control the "experience," which they’ve wanted to do for a long time, but have allowed security vetting (driver signing, for example) to be haphazard at best.
Don't think that Windows 8 on tablets will be your current PC on a tablet; Microsoft won't let tablet sales cannibalize their desktop/notebook sales. You may use Windows 8 on each device, but you probably will learn to shuck your old licenses and apps in favor of new ones. Or at least that's what I think their bet is.