Motive ? Id say your own father sentencing you to death for a crime he knows you didnt commit and everything else we have seen or heard is motive enough. I agree the book version is probably better but I don't think the TV version is terrible either. I like the fact that it is a character we truly know and see (Shae) that pushes him over the edge rather than someone telling us about another character. Show, don't tell as they say The relationship between Jaime and Tyrion however is different and I guess we will have to see how that plays further down the line. I do prefer the book version, but I don't have a problem with how it has been adapted.