Look, the desktop is not dying in any way, shape or form.
The "problem", if it can be called that, is three-fold:
1. Desktop computers have been commonplace for over twenty years now, so practically everyone who wants one already has one.
2. The upgrade roundabout has slowed down massively: a ten-year-old PC ago is still sufficient for most of today's consumer tasks (despite Microsoft trying to change that with Windows 7/8). That certainly was not the case ten or even five years ago.
3. PDAs are outselling everything else at the moment for one reason. We are in an adoption phase for both tablets and smartphones. When everyone who wants one of these has one, the growth will level off and settle into a more stable replacement/upgrade cycle. The current adoption trend leads to an impressive growth curve that some dimwitted analysts have tried to extrapolate.
So while we're seeing slower adoption rates of desktop computers, that has nothing to do with people stopping actually using them.