I wouldn't take it to mean that PCs are in decline. I would just take it to mean that nVidia recognizes mobile isn't going away, and that there is a lot of money to be made there. That's doesn't necessarily mandate the death of the PC. I don't think that anyone expects smartphones to disappear, and I'm still puzzled as to why so many are so anxious to see their counterpart machines that can facilitate serious work (or play, for that matter) go away.
I think the idea is that there are orders of magnitude more content consumers, than content creators. To a greater and greater extent, mobile devices are fully capable of displaying all the content you might want (tellingly, the exception being high-end 3D games). Once traditional PCs are only useful for content creators, the economy of scale for manufacturing those systems may no longer apply.
