just to be 10000000% correct, they are called out for a perceived bias in who they attack. not that they are inaccurate in their information or criticisms.
They just attack the same side, same people all the time. So I do not believe it is "perceived" bias, I believe we can just call it "bias".
Why call it "perceived". Are you saying that Stewart & Oliver are not agenda driven. That would be like someone saying "The perceived bias of Rush Limbaugh".