Second - Does that mean that if I write a novel that is made into a movie, everyone has to speak with an American accent?

I think that there is a good argument for the Hobbits having a British accent, but what about the Dwarves? Or the Elves? Or the Dunedain? Or the Rohirrim?

The speech of the Hobbits was said to have sounded very strange to the people of the south. This would imply that the accent was totally different.

I think that if you make a movie that spans an entire continent and EVERYONE speaks with a British accent, then THAT will be the unbelievable thing.

I'm not saying that some people SHOULD speak with an American accent. I'm just saying that in no way whatsoever is it a cause to deny a part to an actor. After all, isn't the definition of the word "actor" someone who pretends that they are something they're not?