Whitewashing Baskerville

Watching a 2002 version of The Hound of the Baskervilles, with Richard Roxburgh and Ian Hart. For some reason, they decided to alter the legend of the hound - instead of the ancient baronet kidnapping and raping a young village girl, who perished fleeing from him across the moor, now he falsely accused his wife of adultery and was killed by her faithful hound after she perished fleeing from him etc. They also decided that Selden the convict was spared because he was 16, and have Stapleton murder his wife, shoot Watson in the shoulder when he comes to avenge her, escape across the moor being chased by Holmes, taunt Holmes when he falls into the mire, and be shot by Watson, who then has to rescue Holmes...

I always wonder why the heck they make such changes, especially the minor ones, like to the legend.