the reason they left out the jamie and whore thing is because of the television format
in a visual medium any characters mention off screen have no emotional connection
So Tyrion being mad about that other whore, wouldn't connect with what has been established in the show, even though they mentioned, we never saw the events on screen, so there's no connection.
Tyrion's emotional connection is with shae on the show because that's what we have seen on screen
that's the problem with taking books and turning into visual medium, unless the writer of book wrote it with intentions of it being translated into a visual form, you will always have these type of problems.
the other lil nikka died by the skeletons, simply because they probably felt he wasn't important enough to keep paying