[Bluestrike2]

> Apart from the chore of shifting, and the added investment of an extra set of rims [...]

The former is probably the biggest factor, with the latter taking care of the rest. All-season tires might be less-than-optimal tires in either summer or winter (though the higher-end ones have gotten much better), but the perceived convenience factor is a big enough selling point for most. And when their performance isn't sufficient in winter, people probably aren't going to immediately blame their all-season tires for a loss of traction. They'll just blame the weather and assume that "it is what it is," even with AWD.

If you've never driven on proper winter tires when the weather goes to shit, you don't even know what you're missing. But more than that, I think there's a huge segment of the car-buying public that doesn't give their tires any thought beyond "are they still good?"

Hell, my sister bought a Mercedes a couple years ago that happened to come from the factory with high-performance summer tires and no mention of that fact on the build sheet or window sticker (nor was it spec'd with large wheels with low-profile tires, where it'd at least some sense). Had I not looked at the sidewall when I was with her after the tire pressure sensor went off, she'd have been in for one hell of a dangerous surprise when the first winter storms hit a couple weeks later. Even the dealer was surprised by it.

Ever since then, I've always wondered just how many cars drive around in winter weather with the wrong tires and a blissfully unaware driver.