@sozobe,
I've known about these for years, haven't seen it where I've lived lately, but then I don't know my present city as completely as I knew Los Angeles. South LA used to be famous for this, having miserable bus transportation and few if any regular grocery stores. That was back then, it may be different now.
I also noticed that stores that did exist in borderline poor areas had dismal produce sections in contrast to stores elsewhere - but that is just anecdotal, from my own experience.
Anyway, when I read that article, I wasn't the least surprised.