Don't something like 80% of Americans live in urban or sub-urban areas? I live in a suburban area in Europe and have no problems getting around with public transportation. I get my groceries delivered by the shop.
A typical suburb in the US will have no public transportation, and be so sprawled out that bicycling or walking between places would be impossible for a working adult.
In America, most suburbs are bad for walking, actively hostile to biking, and have either no public transit or nearly unusable public transit.
The cities are usually not much better, either. Only a handful in the US have public transit that can even be called decent, let alone good.
Personally, I've lived in many cities, suburbs, and rural areas in the northeast US (population-dense, relatively friendly toward ecological initiatives) and tried to use public transit whenever possible. My experience is that public transport outside cities is practically nonexistent. In cities, there are only buses and they're annoying/slow/don't go where you need them.
Only now that I live in the immediate vicinity of Boston do I have useful public transit options, yet still, owning a car is a necessity to get to anything outside the city.