Tablets are toys.
The form factor is made for either consumption of media, basic control panel use, or amateur content creation.
Working on a tablet is slow.
PCs are work horses. They aren't going away any time soon.
Keep in mind that many new tablets are coming out with hdmi Ports and USB host ports, meaning they can potentially be turned into a mini pc.
As portable cpu's become faster, and apps become more functional, tabs will replace cheap PCs.
Perhaps this is what Microsoft is all about with windows 8. It's about the only thing that's going to save windows 8. Otherwise it's terrible.