Well, I live in SF. As you say, I have several grocery stores within 0.5 miles of my home. The problem? I live on top of a hill; the stores are at the bottom. There is absolutely no way I'm lugging grocery up the hill on foot or on my bike. What about public transport? There is a long wait (muni sucks, esp where I live), and then there is still a bit of lugging to/from the bus stop.

Grocery shopping is literally the only reason I still own a car and pay ridiculous city insurance rates. I don't use it to go to work, meet friends for dinner/drinks, or anything else for that matter.

And then of course, there are times when I couldn't be arsed to go grocery shopping :)