Fallows does it eloquently:
In their current anti-NPR initiative, Fox and the Republicans would like to suggest that the main way NPR differs from Fox is that most NPR employees vote Democratic. That is a difference, but the real difference is what they are trying to do. NPR shows are built around gathering and analyzing the news, rather than using it as a springboard for opinions. And while of course the selection of stories and analysts is subjective and can show a bias, in a serious news organization the bias is something to be worked against rather than embraced.