It comes down to games. The number one purchase of PC's is for games. With the windows platform, you can build a custom PC that will run all of the games that people want to play. It's a sad reality that this is what people want to do, but I'm glad they choose the PC platform for this endeavour. Another reason is platform specific applications like Autocad. These applications run on Windows and not the MAC.
Who really cares what the average user wants to use, how many times have people asked you what to buy for a computer, just to go to the nearest outlet store and buy crap from someone that has no clue! You get what you pay for.
Besides, crashing, virus infested, registry corrupted PC's keep many people employed!
Do People Who Don't Know How to Use Computers Choose PCs?