What's with the British Accent?

I recently watched "Valkyrie" and realized Tom Cruise did not even attempt to do a German accent, but the audience assumed that he was in fact German. The rest of the German soldiers had the all-too-familiar British accent, which lead me to ask, "why Hollywood, why?" Cut to any kind of ancient Rome movies/shows, "Rome," "Sparta," and "Troy" - ALL British accents.

Over the years I have realized how much it gets on my nerves. Why can't you do an entire movie in Latin? What's wrong with keeping it historical and more realistic? I had to applaud "Passion of Christ" because the actors actually spoke in Aramaic, Latin, and Hebrew. In "Braveheart" everyone had Scottish accents so therefore the movie was much more believable. I think Hollywood makes movies and thinks, "ok, this doesn't take place in America, British accents, everyone!"