Not only is it impractical in rural areas of the US like others have said, but in most small-to-medium sized cities as well. Some places simply won't hire folks if they don't have access to a car. Some small cities have no taxi service, and the larger (30-80k) that do often charge too much to use on a regular basis.
Not to mention the same holds true for rural areas of other countries as well, as the bus system might not come often enough to work, let alone buy groceries. Or you might have to deal with weather which makes bike riding (let alone walking) inconceivable.
Where I live, the closest store is 5 miles, but it's just a very basic and small general store. To reach an actual store with fresh produce and more, it's a 100 mile round trip. That may be on the somewhat extreme end of things, but variations on that are a normal way of life for people in rural areas.