actually, uk supermarkets have far more ready meals than us ones, at least where i live.
they have great deli bars, with prepared food, but all those aisles of 'ready to heat' chinese etc. don't exist.
yes, they do cake mix etc, but so do british shops. there are also specialist food stores (both food suppliers, and of equipment) which do VERY well, so it can't just be a small minority that cook properly. the big difference i've noticed, is that eating out is much cheaper & far more relaxed, so families will go our for a meal at weekends as a 'normal' thing, rather than as a special treat.
also, places like kfc, macdonalds, are out of town places, for when you're travelling around, going out for dinner is more likely to be a small independent place in the local town, rather than a chain.
i suggest you google whole foods or williams - sonoma if you want to see the other end of what is on offer. you could also email a tourist centre for a city, asking for recommendations of places to eat. see what you get back. the uk image of corporate america is warped. yes, it exists, but it is a lot less prevalent than we imagine.