It seems to me that all things wear out, even pc's. Also in a lot of industries, new software requirements require systems to be kept up to date in order to process the new software updates. Our business replaces every PC after three years of service. This keeps us up to date and functioning at top levels.
Yes, things are much cheaper. As with everything electronic, they become cheaper with time. Anything new, such as phones with ability to take digital pictures will be cheaper next year. And every time some new device is invented, more chips etc. will be required to produce and make the item function.
If I am missing somehting in this picture please let me know. Some of the nations that trail the advanced nations have yet to upgrade or acquire the PC's for their functions. The world will continue to acquire PC's.