Parking - Its all about the parking! And opening hours.
I'm increasingly convinced that the best method for acquiring food will be to do a regular "big" shop online for long shelf life type groceries and other household supplies. Stuff that comes in a box/tin/packet and you don't need to select in person or buy fresh.
Then a much more frequent daily/every other day shop at a small local place to get fresh fruit and veg, meat, fish etc.
Best of both worlds, cheap groceries and high quality fresh produce.
But very few local shops currently offer this opportunity mainly because the opening hours are pathetic. Look to the continent (Holland is a very good example), most shops are open into the evening so that people can do their shopping on the way home from work (on their bike). Here you are lucky if the local shop stays open past 4.30 and going at lunch isn't a good option as you have to pay £2.50 to park.
Sure supermarkets do some fairly dodgy things to get their shops built but it is the crappy British local shopkeeper who let them be successful.