That'd only be a valid analogy if 50+% of the driving population didn't use or particularly want windows. MP gamers have had run of the gaming world for some time, partly because the gaming press is full of them (by their very nature gaming press are going to have friends that game and have time to play games with them, so you get a severely disproportionate view). The fact is that even a lot of people that play exclusively multiplayer games (like WoW and Guild Wars) play single player the entire time. MP most decidedly is an extra, and a totally useless one to a lot of folks. We may be used to getting hosed by being charged for incomplete SP experiences, but that doesn't make it right.
You are living in the past.... multiplayer is not the result of some evil scheme. Multiplayer is wanted by people because it is infinetely more fun to play against humans than it is against a machine and is made possible by the internet. Eight million people playing an exclusive MP game (WoW) would maybe give you a hint of that.
For anything from tennis to chess people in general enjoy playing against real human beings rather than an AI. And you know what, they arent mutually exclusive. Most games have both an SP component AND an MP component so you can do both, depending on your mood.
And that I Im sure is what the majority of gamers want. The ability to play SP and MP. And as I said in a post above. The idea that an MP component would ruin the SP experience can be said for any component. Too much effort put in the GFX component could make the sound component crappy, too much in the AI component... and so on.