It's not either of those reasons, it's that the story is old. Over and over again, the same thing appears:
US soldier killed
Atrocities planned by terrorists
Mistakes made by US soldiers
These networks want ratings, not to put out the news. If Tiger Woods' latest confession gets people's attention more than the boys in the sandbox, it would only make sense to put Tiger Woods on the news. There's no conspiracy, just a truly disheartening product of the free-market news model (a model which I support, however).
-Penguin