The basic distinction has already been covered, i.e. ales (top-fermented) are served cool and lagers (bottom-fermented) are served chilled. The American jibes at 'warm beer' are just that, mild insults that started out as knowingly untrue just to get an annoyed reaction, such as by GIs during WW2, and were repeated by those who didn't know any better.

Getting beer straight from the 'old country' is no guarantee of getting the genuine article. Often you get an 'export' version, which is made with extra hops so you can still taste something when it's been chilled. Probably the best way to avoid it is to buy something from one of the smaller breweries who can't afford to make an export beer especially for people to chill. To be fair, there are plenty of places in the USA that get so hot that there is no chance of having a cool cellar in summer, but most beers will survive in the fridge without unduly spoiling the taste.