Combining those two paths back together is what a lot of technologists are keen to do, and some of those technologists really
love Windows and the PC and really
want that path to come back together again.
That would be a mistake. The schism is helpful. It allows us to have machines that are great for focused work, together with a clear path of opportunity going forward to make them better. And it allows us to have great devices that can make our lives more fun and engaging, and it also has it's clear path of opportunity going forward.
(The Windows 8 Project, with Windows RT, Windows 8, Metro-style/whatever-style, and Surface highlights this problem by showing what happens if you do try and combine those two worlds together. Even if that combining is done with skill and care, as I'm sure it was.)
So we shouldn't combine them. PCs are great at what they do, and lousy at the other stuff. The reverse of that applies to post-PC devices too.
This last point is why no one is ever suggesting that people replace PCs at work with smartphones and tablets. That makes no sense. PCs are really, insanely great at the work stuff. Post-PC devices in that context would just get in the way. How post-PC devices help with our work lives is a) complex and b) a story for another day.
Keep 'em separate. And a smartphone is not a PC. And neither is your tablet. Your PC is, however, a PC.