it's the same with ALL networks - from travel to cooking to dancing to news.
you put on the stories/people that will elicit the most emotional reaction - either love or hate.
It certainly wasn't newsworthy to show Rev Wright footage for 6 straight months - okay, we know the story. But wow, every time that clip was shown, FOX viewers' blood would boil and they'd watch for sure. MSNBC/hardball is like that too - Palin or bachmann on almost every night as topic. People love rooting against someone they hate, and they LOVE when a story is coming up that makes this person look bad. The palin story is usually at 5:50.... so they make you watch the whole hour with plenty of teases.