I think that the changes that were made with Jamie are to do with not alienating a TV audience. Several hints were dropped about Jaime in the first 2 books, but they were much more subtle except where Tyrion is concerned. It was made very clear that Jaime loved his little brother.

Renmure Tully = sheer genius.

Sam Tarly = Win and Awesome, always and forever.

I wonder if this is how hardcore Lord of the Rings fans felt in 2001.

Ditto.