Exactly -- more power to you, save gas for when you need it -- I got no problem with a gigantic SUV when you need it, for long trips or off-road or hauling stuff, but to go 10/15 miles to pick up a carton of milk? That's where this little thing would be useful.
Cars are like any other machine. My MP3 player is not a replacement for my living room stereo or car stereo. A pair of hand snips are good for trimming bushes, but won't replace my lawnmower. Because cars are so expensive, we tend to compromise -- but if they could get inexpensive enough I would love to have multiple tools, each tailored to the job at hand.
Right now, I have a '99 Sebring convertible. It' a lot of fun to drive, has comfortable seating for four adults, good trunk space, and not bad economy. I expect to get an '83 VW Vanagon camper in good shape in the near future -- I can use it to go camping, or to carry stuff that won't fit in the trunk of the Chrysler.
Some planned communities have "neighborhood vehicles," basically golf carts, with paths for them. It's not a bad approach. And I live in a moderately dense suburb, so I'm not talking about 10 or 15 miles to get a gallon of milk, I'm talking about 2 or 3 -- a bit much for a walk, not great for a bicycle, scooter or Segway that has you out in the elements on a cold or rainy day.