In my medium-sized, nondescript town in Hertfordshire, UK, there are Chinese, Thai, Indian, pizza and Italian restaurants in particular. There was a Mexican place, but it's now a steak house. Probably one or two kinds, but we don't eat out particularly often so I don't know for sure. Most pubs serve food, which will generally be of the 'British' kind, eg a carvery, shepherd's pie, fish and chips etc - and somewhat to my surprise there are two pubs that offer Thai food. There are a Chinese and a Thai restaurant in the middle of town that offer a buffet at a fixed price, so essentially portions are whatever you want - there's also a mixed cuisine restaurant with a buffet on the same system, so that one of you can have curry, another Chinese and someone else a roast or pizza. Useful if you don't fancy the same thing...
There are quite a lot of take-aways, too, from fish and chips to Caribbean.
As for portion sizes, well, they seem reasonably comparable to me. I have found that very high cuisine does come in tiny portions (google The Fat Duck!) , and I certainly wouldn't describe anywhere here as being in that class. I dare say a meal in a smart Italian restaurant wouldn't be quite as filling as a meal at a pizza place, but there's not a huge difference.
I did go to a restaurant in NYC called 'Southern Hospitality' (I think); my friend and I ordered a one-person meal which was a selection of different meats, if I remember rightly that meant pork ribs, braised steak (omnomnom!!) and chicken, and we couldn't finish it between us. I've never been offered anything quite so huge here—although there may be items on the menu that are *enormous*, they advertise themselves as such, rather than simply turning out to be too large for one person to eat.