There will always be a damand for stationary systems. They are usually the most powerful type of personal computer. They are far more standardized and customizable; most of the components in notebooks, tablets, PDAs, etc. are all proprietary and follow few standards like form factor and expansion.

Oh and comparing PCs with Macs is literally like comparing Apples against Pears. The only difference is the OS and the case design. Their OS can be put on pretty much any white box with enough effort or none (depends on driver support).