I saw True Grit just last night, and the lack of contractions struck me as well. Another place you see this stylized speech depicted is in every single last portrayal of Robert E. Lee (and really, just about every other Southern general, and many of the Northern ones as well). I may be wrong about this, but something in the back of my mind says that the correspondences from Lee and others actually were noticeably lacking in contractions. If that's the case this may be due to what Martha (I think) mentioned as the perception that use of contractions was for the ill-bred. They'll be showing the Civil War documentary again soon on PBS, which features readings of excerpts from many letters and diaries. I'm going to have to listen for the contractions.