Serving temperature is largely dependant on flavour source/dominance.
There are basically three sources of flavour in beer: hops, malt, and yeast. They work together to form a (hopefully) cohesive whole, usually with two supporting the other (sometimes by stepping aside and getting out of the way).
Most beers, and especially American ones, tend to avoid yeast flavours, with lagers being especially clean on this front, and ales picking up a little more -how much depends on the style- and a few styles, such as saisons, being unlike either lagers or ales in that their primary flavours are from the yeast, with hops and malt playing second fiddle (track down some Saison Dupont if you're curious).
Malts play a larger role in ales than lagers, though they do play an important part in some of the latter (dopplebocks spring to mind). It is essential for barleywines, porters, stouts, Scotch ales, and milds, among others -- a barleywine without a huge body and a big malt hit simply would not be a barleywine. There is a wide variety that one can add to a beer, offering anything from a nearly tasteless pilsner malt to the flavourful Maris Otter, with specialty malts supplementing them with the sweetness of crystal malts, the, err, roastiness of roast malts, and more. British beers are generally on the malty side of the spectrum.
Hops provide bitterness (and act as a preservative), but can also give spicy, flowery, or fruity tastes, depending on the variety and brewing techniques (for a given quantity of hops, there's a tradeoff between bitterness and flavour, with the only way to get lots of both being the use of lots and lots of hops, which can be expensive). Lagers tend to get a lot of their flavour from hops, and some ales, such as India pale ale (originally made to be shipped to India, highly hopped to help it last the long journey), are also hop-dominant. American breweries, including microbreweries, are mostly quite hop-focused, with their takes on styles being noticeably more bitter than their European counterparts.
Now for the actual point of this post: The lower the temperature, the less you taste the malt, and the more the hops comes to the fore (although after a point you start to dull the entire taste). Colder beers can also be more refreshing -- if they're designed for it. A barleywine will be served relatively warm (ten degrees is a ballpark number; its comparable to port wine) so that you can get a full bite of the complex maltiness and to suit the freezing winters night, while a pilsner will be served relatively cool (four degrees or so) to bring out the hops and be perfect for that sweaty summer day, and crud like Corona will be taken down as low as possible so that you don't realise what you're putting in your mouth. This is why there is some difference in average serving temperatures between your continents, but there are so many varieties of beer that stating 'English beer is warm' or 'American beer is freezing cold' is like generalising the serving temperature of food -- from soup to icecream.