Never really understood the "cannot afford snows" thing. You're not really buying any more tires then you would have used anyway. The cost is just front loaded since you buy two sets now instead of one now and one later. Your summers aren't getting worn out when you're using your snows and vice versa, obviously.
You gotta pay to have them swapped or put them on rims I guess, but you still shouldn't be using any extra tires. I know many places you of course don't really need the tires, but when people say they can't afford them around here I just don't think they've actually thought it through. And the roads are so poorly taken care of in this state I frankly don't understand why anyone bothers trying to get by without them.
As far as the expense of snow tires, you're right, it's only $500 or so for a complete set. Not a huge extra expense for most people (although it could be for some).
Whether it's good value is another question. Certainly they're good value if it snows often where you live, and you drive a lot.
Remember though that some people live in areas where it snows infrequently and some don't drive every day. They could get by with transit or telecommuting on really snowy days, for example. Also, it can be a hassle to go and get your tires swapped for just the few days you really need snow tires.
One poster also mentioned storage - could be tricky storing your other set of tires if you live in a small apartment rather than a house.
Anyways, the bottom line is that these combo tires are great for their intended market - people in areas of infrequent/occasional snow.