They tend to be the convenience option though. There isn't a greengrocer near where I work, and only 1 on the market where I live. There is an Asda, a Tesco, and Morissons within 1/2hour urban drive to work, and a Tesco, a Sainsburys, 3 Asdas, a Morissons, 2 ALDIs and 3 LIDLs within 15minutes drive of home. The market opens 8.30-4.30. Even the shortest opening supermarket, they stay open until 8pm. If you work outside the town centre but live close to it, they are the only real option.
I agree with that, when I lived in Luton we always used the local indian shop as they had such a fantastic range of all veggies.
Now, in Warrington, there is an indian shop, but he tends to only stock exotics (yams, aubergine, okra, mouli), chilis, and loads of herbs. But when we need anything he stocks we go along and it from there.