The Empire and the Sith are not the same thing. First. Second. The people in the empire are more regimented cuz failure often leads to death from the Sith. So they speak in a more regimented way ie. "proper english". But the people in the empire other than the sith are not neccessarily evil. They are just working for the good of their government cuz they think its better than the republics form of govenment. So empire voices should not offend you as a british person cuz the empire isnt evil. Its just lead by evil people who, by the way DONT all have brittish accents. So dont worry, bioware doesnt think you are evil.