People do shop at supermarkets via bicycle
(See "Zoning Commission Chairman: No One Bikes to the Grocery Store" from the Washington City Paper.)
Yes, I am willing to concede that large families would find it difficult to shop this way. But that demographic isn't typical of center city households.
In fact more generally, household size is shrinking nationally, and in the city in particular. See "In USA, more choose to live alone" from USA Today.
I will say that the quality of bicycle parking at supermarkets tends to be pretty substandard overall. (More about this some other time.) This Giant is a bit better than most.