So what is stopping us from setting up an online store that provides goods and services from these supermarkets
@Paul, IMHO, for such a store to have a chance at success, it would need to have access to those Supermarket's catalogue database. Then, you need to find a seemless way for customers to pay and a delivery mechanism that works.
I think the reason such online stores have failed in the past is because they attempted to duplicate the supermarket's catalogue, i.e. you go to uchumi, get items and prices and re-enter them into your application.
The delivery mechanism has been proven, courtesy of the Pizza delivery guys, payment methods are quickly maturing, e.g. pesapal, so now its for a clever person to convince these supermarkets to open their data, which I think will not happen soon.