You're forgetting one little, tiny detail: all the content for tablets and smartphones (movies, television shows and ads, apps, etc) is PRODUCED ON DESKTOP COMPUTERS. As long as that's the fact, we'll keep using a huge amount of PC's. I think that what you are meant to say, is that from a consumer standpoint, the PC era is over in the sense that the media content and activities are done via tablets and smartphones. That's is true. So, as long as you're not involved in any kind of productivity area that involves PC's (I work on film editing and 3D design) and you only consume content instead of creating in, well, you're nice and tidy on a tablet and a smartphone.