Because everybody knows that the Aramaic language Jesus spoke sounds strongly like Eliza Doolittle in Pygmalion:

“Bless'd are 'em what are poor in spirit,
for 'em is what gets th' kingdom of 'Eaven.
Bless'd are 'em what mourn,
for 'em will be roight comforted.
Bless'd are 'em what are meek,
for 'em is what will in'erit th' earth.... :D

Largely, but as Bethberry says, not wholly. And I think a lot of Americans (for example) still retain a very strong sense of their heritage which could have been from a number of places - Germany, Norway, Russia, Italy, Ireland...etc... Though with the main language used in the New World being English then if people from all kinds of places did look back to the origins of the English language, that goes to show how powerful an influence language was over a whole culture, even a new one.

Again, I wonder if things are different in say Montreal, New Orleans or Florida, which had other, stronger language influences than English. Would people with a long background in these places automatically think of English if they cast their minds back to the years before the Americas were colonised?

It's interesting though, that representations of 'medieval' culture from modern American (or made with the American market in mind) films, TV etc often have a more Germanic/European feel to them than an English one, despite the language. The knights are more elaborately fitted out, more colourful, and there is much more pageantry. This all came quite late, really, to English kings, as they were so busy killing one another for the throne or killing other kings and 'saracens' from 1066 onwards.

You can at least do Eliza justice - her pronunciation wasn't half that good! :D

Well, since knighthood never had the chance to enter America, all of those films have to have a Brittish accent (the ones about knights). And I suppose the rest kind of followed.

Film is a visual medium. The more elaborate something is the more visually impressive.

And accuracy has never been very high on a film-maker's to do list.

Not necessarily– but we are talking about English-language productions, aren't we?

And it helps distinguish it from all those ultra-cheap 80s sword-n-sorcery flicks...

Does it need to be impressive though? A Game of Thrones is a huge success but it's quite low on the visuals, compared to most US output. The joust scene in the first series was hardly epic, more like something the BBC would turn out - and I think the producers of the series Merlin would have made it more 'visually stunning' (and the books give the impression of lots more colour/pageantry, too). An amazing script and cast can mean the SFX and art department needn't cost mega bucks. Also see: Robin of Sherwood for high impact but less showy 'historical' drama.

I think it's because there are different perceptions or audience expectations of the period, not always, certainly nowadays, limited to which country is making the drama, but in the past it seems to have been. It might be a British thing to react with distaste if something isn't accurate (I couldn't enjoy The Kings Speech for example because it's simply wrong). Certainly our re-enactment societies are a completely different kettle of fish to the fun that seems to be had at Ren Fairs.

While carefully spending precious homework time on the olden days of the Downs, I stumbled onto this post by SPM where he quotes the Letters with Tolkien's own opinion on accents:

Interesting you should mention that but it is a factor regarding Game of Thrones that the critics almost always make mention of what they tactfully refer to as "budgetary constraints" which is newspeak for "We want things to be more showy."

For the most part I agree with Lalwende (except maybe about the HBO thing, in my area HBO is bundled into the standard cable package, you have cable, you have HBO, and I imagine similar arrangements exist in a lot of other areas of the US. but no matter.) If I may use a non-Tolkein example; amongst my collection of well loved audio CD's are a selection of adaptation done by the Atlanta Radio Theatre company of some of the stories of H.P. Lovecraft. One of the big reasons I love these recordings so much is that the Atlanta Radio Theatre company actually took the time to make the accents sound appropriate to the characters given thier region and characters. Armitige sounds like a Boston Brahmin (which is I suppose as close as you can get to a real world to the accent of an Arkham academic), Obed Marsh sounds like a Nantucket Whaler/Shipper (aka a "Captain Ahab" accent) etc.

Do you mean like Charles Emerson Winchester III from MASH?

Or Katharine Hepburn referring to her fondness for callalilies.

Actually I meant a little like Ted Kennedy; I think I may have gotten confused as to what a "Boston Brahmin" accent is. Larchmont Lockjaw I'm good at, but I get a little foggy outside of my range.

Dwarves!
 

I thought of an example when an accent used in a fantasy setting wasn't British.

In the Dragon Age universe created by Bioware for their game series of the same name, the dwarves are given American accents. The dwarf party character from the first game, Oghren, sounds like he came straight out of West Texas.