http://winteriscoming.net/2014/05/23/characters-confirmed-game-thrones-season-5-new-details/What? Maggy? They're including that bullshit! No!
Seriously, the whole subplot about Maggy and her prophecy was a really bad move on Martin's part. It basically destroyed any complexities or subtleties to the relationship between Cersei and Tyrion. There were so many interesting potential explanations of Cersei's animosity towards Tyrion, all relying on her warped psychology. Was it simply because he caused her mother's death? Was it because she felt that she had to compete with him for Jaime's attention? Was it an unconscious attempt to imitate her father, whom she both admired and resented?
No, actually it's none of the above. See, the real reason that Cersei has always hated Tyrion is because long ago she heard a prophecy basically saying that her younger brother would destroy her. That's it. Nothing to do with their family or the complex emotions that people experience or anything like that. Hell, that kind of thing might be understandable, or even relatable, and we can't very well have that, can we? Nah, so much better to say that it's just because of some bullshit prophecy that Martin pulled out of his ass at the last second. And now the show is actually going to include it.