Part of the reason for "US culture" (specifically: not walking mostly) is that zoning laws largely prevent over/under residential/storefront construction.

This makes everything so far apart as to make walking inconvenient. Add in unbearable weather for half of most years (whether hot/cold), and it just isn't convenient to grab something "on a quick walk" from the grocery store that is miles away from most homes.

Thankfully (some) cities are beginning to realize this, and are changing (IMHO: stupid) zoning/regulations. My favorite example has been of my own hometown's (Austin) reduction in required parking spaces for most commercial activities. This increases density, and encourages more walking. ATX's buslane-onlies leave a lot to be desired... but at least they've gotten rid of (most) downtown oneways.