Doing something and doing it well or easily are two different things and again that is the gray area. Do you really think an architect or engineer would use CAD on an iPad as the primary device to accomplish professional designs. I don't think so. They might use it to review a drawing or make a minor adjustment in an emergency but with much more difficulty than on their PC. iPad is a very big compromise for the sake of novice users and portability. If it is defined as a PC it is the most crippled one ever made.
You're missing the point. You use words such as primary, but that's meaningless. Would they use a netbook? Of course not! But that doesn't matter. My CAD app works very well, and I use it to design parts. It's great! I can work on them wherever I am. Too clumsy on a notebook.
Verto Studio, look it up if you have any understanding of CAD.
Even many notebooks aren't going to allow a major use of CAD, but that doesn't mean they aren't computers.