I saw the other StarWars question the other day, and earlier today something hit me. Most of the rebels spoke in an ‘American’ accent, but the Imperials spoke in an ‘English’ accent. No biggie, but when you think of it, most of the rebels were originally Imps. So how did they drop the accent so fast? I’ve known English people who’ve spent the last 45-60 years here in the good ol’ U.S. of A. and haven’t lost their accents… I just can’t figure it out.
I believe they were able to drop the accent so fast because the ACTORS they hired had American accents to begin with and had possibly never even been to England before, so I’m guessing it was quite easy to do. 
OK, really quick WAG.
For an American audience, proper British accent = evil ones you should free yourselves from.
Redneck accent = cool dudes you can identify with.
I’ve been thinking about that answer for a while, and that’s the best way I can explain what’s going on in my head.
Ok, you have to remember that a lot of the main characters (all except Leia) weren’t in the Empire, Luke was a farmboy, Han a smuggler, and Chewie… well, I’d love to see a wookie with an english accent. IIRC, most of the pilots were not in the imperial navy before they joined the Rebels. The ones they talked to I mean, many of their squadrons were defectors.
[Thumbwars]
“Why do we all speak with British accents when we’re from outer space and there’s no Britain?”
[/Thumbwars]
Andyman could have a point there,
Come to think of it, a lot of British speaking actors in american films(not all, by far) play villains…
Just some films with a clearly distinguisable badguy in a row:
Remember the Lion king?
Remember Scar’s accent?
Mission Impossible II?
The bad guy spoke some sort of british English there
Gone in 60 seconds?
(well the bad guy there even was european…)
Have we stumbled upon a stereotype here?
Yes, we have ;). Eddie Izzard makes a pretty good statement about this: “We play bad guys in American movies because of the Revolutionary War.” He then goes on to do a hilarious routine about how the Empire all had British accents.
Darth Vader doesn’t have an English accent. It’s just the “JEJ voice of doom.”
Jman
The bad guy in Die Hard had an English accent, and he was named Hans Gruber.
But what of Picard?
“I say, GROOWF!, old chap…”
and JMan… Darth Vader had an english accent once Luke took his mask off. Figure THAT out.
What I love is how Leia has an english accent (slight) while she is held on the Death Star but this falls by the wayside after she is rescued.
Yeah, but Picard was also supposed to be French. 
…Which is precisely why you never saw Picard and Darth Vader at the same time.
AND, Vader is also bald.
I rest my case.
ROTFLMAO!
Have you all forgotten Obi-Wan Kenobi? British accent, good guy.
Actually, Moff Tarkin (Peter Cushing) spoke with a English accent, but most of the other Imperials didn’t. I remember the doofus that got the psychic stranglehold from Vader seemed to sound American. So did all the stormtroopers that got to talk.
I’m not sure what kind of accent the Emperor had, but it wasn’t British. Sure, Palpatine sounded that way as a Senator in the Phantom Menace, but he was just weird and scary sounding by the time of Jedi.