The film "War Horse"

My wife and I went to see the film "War Horse" this afternoon. A reasonable yarn, but several things annoyed me. Why do film producers (and the BBC for that matter) choose such strange "local" accents for people supposed to come from Devon? Why were there lots of conifer plantations on Dartmoor in a film set before/during WW1? Why was the Devon village made of Cotswold stone? Why do we have to have "American deep" music to portray pathos? Why did I keep thinking about all the CGI effects? Why did Spielberg bother? Why did we bother?