I think Microsoft vastly overestimates the perception of the term "PC".
In their latest commercial, Microsoft snarkily has Siri saying "Wow, you're a real PC" to the competing Windows tablet. I suspect most of the general public would associate the term "PC" with complication and frustration however. A PC is that clunky thing that never works like you want it to. That has problems printing the document you need right now. That runs slower and slower day after day. That constantly nags you to update this or confirm that.
Is that really the image you want for your new product?
I think Microsoft is on the right track by trying to show the strengths of their platform versus Apple's, but the folks in Redmond still have their heads in the 90's. The PC is no longer cool or innovative. It's the old clunker we're all buying tablets to replace.