I think counting iPad sales as part of the PC sales is entirely the right thing to do. You can be sure that if other manufacturers had ever had success with Windows tablets that they would have been counted as PCs, even if they were mainly being used to consume media.

And sure a Windows tablet isn't exactly the same as an iPad, but they potentially fill the same niches for a lot of customers. I know alot of people think that the iPad is just a big iPhone without the phone, but I think history will record that it fits into a PC shaped niche, not a phone shaped niche

However, I think getting excited about Apple's PC market share including the iPads is a little premature. There are plenty of people out there who wont buy Apple or who will just buy a tablet if it is cheap enough and there is enough "buzz" without taking much care to think which tablet it is.

Until there is some competition there is no way of predicting what the Apple share of PCs including tablets will be.