I believe that the home PC market would not be what it is today without MS, Well, the home PC market would not be what it is without some company that built an OS. That it was Microsoft had to do with the fact that Mary Gates, Bill's mommy, sat on the board of the United Way with an IBM vice president.
The reality is that the PC market was driven not by Microsoft, which just hitched a ride, but by the openness and low cost of the IBM PC.
That is true, but MS was the company that built the OS, or at least expanded on an existing OS. IBM, by allowing their product to be cloned, did a lot for the home PC market. The fact is though, without MS, there would have been no competition for Apples GUI and PC sales would never have reached the point they have today. You are assuming someone would have jumped in and filled the void left by MS if Bill Gates hadn't decided to go off on his own. There is nothing to back that assumption, no one brought out a competing system, ever. Apple doesn't count because they already existed, and their product was too expensive, the other systems out there met quick deaths.
I stand by my statements, but will throw in IBM also as motivators for the PC market(Apples biggest mistake was to not allow cloning).