The authors predict more bias in stories where the outcomes aren't realized for some time (foreign war reporting, for example) and less bias where the outcomes are immediately apparent (a weather forecast or a sports score). Indeed, almost nobody accuses the New York Times or Fox News Channel of slanting their weather reports.
I'm sorry, I just couldn't stop laughing at the idea of accusing a newspaper of slanting the weather report.
Hmm... I wonder if news sources who favor the current party in power tend to predict more sunny days to make people feel happier. Sort of the "is the sky half cloudy or half sunny" debate. Although it would explain why the long range weather report is really hit and miss :)