The traditional temperature for serving beer in England is at the natural temperature of a cellar (basement). That is around 11 degrees Celsius (52 deg F) in England, and it is fairly constant over the year if the cellar isn't heated or cooled. If you are used to chilled beer, cellar-temperature beer would indeed seem warm. Traditional beers aren't artificially carbonated or pressurised either - they are usually pulled up from an unpressurised* barrel or keg by a beer engine - a rudimentary hand pump. People used to drinking cold gassy beer therefore think that traditional English beer is warm and flat. Those of us who like traditional beer think that everything else is cold tasteless fizzy cat wee (no offence to cats, I hope). It is really quite simple.
Then there's all the marketing hype on both sides of the fence...
Best,
Helen
*The barrel is vented to atmosphere via a porous plug, so it is close to atmospheric pressure. The small amount of gas in the beer is what remains from fermentation. In the case of the very rare traditional bottled beers, the gas in the bottle is produced solely during secondary fermentation in the bottle, as is the yeast residue.
PS Please don't take the above too seriously.