Troy

I just watched the movie "Troy" and liked it. A common objection is that it isn't true to the source. The Odyssey by Homer is a story that is about 2500 years old. It was originally written in Greek and was written in verse. It has probably been translated hundreds of times which would likely change aspects of the story. Having said that, movies almost always change the source material. I do however have one question. Why do characters in movies that are supposed to take place in a classic historical period (with the exception of the Passion of the Christ) have English accents?