I grew up watching Jon Stewart and occasionally Colbert. I always thought it was interesting how Jon Stewart would defend against his critics by saying something along the lines of "my show is preceded by puppet prank callers (crank yankers), this is a comedy show first and foremost."

That was his defense against people saying he was contributing to news imbalance or accusing him of not doing anything useful to alleviate the problems of biased journalism. He took a hard line (and still does I think) that he was a comic and was not responsible for anything beyond that.

I remember once he had a segment about a 9/11 first responders bill (https://www.youtube.com/watch?v=FM6cvbjZmQE), which may have reversed the course of that bill for the better (http://www.nytimes.com/2010/12/27/business/media/27stewart.h...).

John Oliver seems to have grasped the power of that particular segment and has, in my opinion, drastically improved the form of the political satire. It will be interesting to see how his perceived influence will affect next season.