To be fair, my assumption on that line was always that they were saying they're balancing out the overall news world. Still dirty, of course. Regardless, everyone knows how they lean.
What grinds my gears is NPR. Every member drive they explicitly talk about how their coverage is fair and unbiased, which is way more egregious than some tagline. As far as having a bias and not owning up to it, I think they're the worst offenders right now.