It had not even occurred to me, but what's really nuts is not only that it could happen, but at current trends, it's not even unlikely! Think about it! Most functions of popular PCs can be replaced by tablets. And because tablets are easy and fun (at least Apple tablets), they will be replaced. The only PC maker not crying over sales of PCs is Apple, and Apple is also the only really successful, so far, maker of the device which will probably replace most PC's, the tablet.
Sure, the chance is also solid that it might happen (Amazon or Samsung may pull out a rabbit), or not within a few years. But it's amazing to think that a couple of years ago, ask anybody if Apple could become king of consumer computing devices, they'd have laughed you out of the room. Many would still try today, but then show them these statistics.