Some dubious categorisation going on here. An iPad isn't really a PC in the same way that a G-Wizz isn't really a car!
Sure it can do many of the things a PC can do, play videos, go onto facebook, and maybe it fits the words "personal computer" better than a real desktop does, but it's still a device primarily designed for data consumption, not production. Sure, you *could* type your entire life story on an iPad, and I'm sure Mr Fry is doing just that as I type, but you'll end up with blunted fingers and probably some kind of compression fracture in all of your fingers from banging on that sheet of glass.
It's horses for courses. Most people don't really need a real desktop PC for what they do. I know my sister-in-law certainly doesn't. She can post up her inane facebook drivel (with humourous auto corrections) just as well from her phone than she can from a desktop of laptop machine.
It just goes to show that many desktop/laptop users didn't really need that full computer experience, so with any luck we'll shift them onto tablet, and the volume of spam email their infected desktop machines were spewing to all and sundry will plummet!