In their defence, Queens English (Kings English now?) or RP was what most (older) Brits grew up hearing from news and documentaries. I'm still conditioned to give more weight to an argument given in a formal accent.

Though I do love how shocked Americans are by the range of British accents. E.g. the pirate, in "Treasure Island" was using a particularly thick West country accent.

Also see "Hot Fuzz" for the best play on accents!