Really? Would you call a 24% growth rate a dying market? Most would consider a doubling every 3 years to be a healthy market. Oh well...
Desktops used to be almost all computer sales, but now they are well below half, replaced by notebooks where most of that growth is, and where Microsoft has more competition. Tablets, where Microsoft isn't a player, are taking over from notebooks. Anybody who can see long term knows Microsoft needs successful diversification. Unfortunately for Microsoft, the attempts to do so have not been very successful, or cost billions in losses just to get to be a solid (but non-dominant) market player as in consoles.
That is why Microsoft's stock is relatively flat. There's not much expectation from the company for new, lucrative revenue sources. Just ten years ago Apple was a bit player in the computer market, nothing else. Now Apple is very successfully into music players, phones, tablets and music sales, and has grown its computer business faster than any other company. This history of successful dynamic expansion and growth is why the stock is so high.
and the growth of specialized products such as all-in-one PCs
So iMac clones are the source of growth. Oh wait, that includes iMacs.
Yep, Apple's sales are counted in that PC growth statistic, including Apple notebook sales which are at a higher percentage than their PC sales. It would also include all those Linux netbooks. So not all money goes to Microsoft. Also remember that Apple makes far more money off of a Mac sale than Microsoft does from a Windows system sale.