There are a few major differences, the largest being that people generally don't have to worry about cross-car compatibility. If each car manufacturer had different driving controls and required a different kind of gasoline, I would bet that you would only have a couple of brands of cars. Still, as Tesla picks up steam, assuming it gets to be fairly commonplace, I think you'll start to see a dichotomy emerge between traditional gas stations and Tesla-style charging, and though there could be billions of different variations of powering vehicles, you won't see many of them being used.
And even so, if you listen to people talking about buying cars, they tend to bring it down to a very selective choice at the end. An individual will commonly come to the point of saying something like, "I either want an Audi or a BMW," and Toyota and Ford are out of the picture. The reason we can support so many different brands is not that people deal well with having lots of choices, but because you have many different semi-overlapping car markets, each having developed their own dichotomies. So there's an "Audi or BMW" guy and there's a "Toyota or Ford" guy and a "Volkswagon or Smart Car" guy and a "Volkswagon or Toyota" guy, each narrowing down their choices to some kind of dichotomy.
Either way, I'm not positing an absolute. I'm suggesting a tendency that's very normal, and is working in favor of Microsoft on the desktop, but working against them in mobile devices. People don't really consider the infinite number of choices that we're presented with. When possible, we like to narrow things down into nice clean dichotomies and then choose between two things.