I think it's important to take anyone to task for failing to uphold their own standards. I think The Daily Show in general walks a fine line between comedy and incisive poltiical commentary, and sometimes falls short of their own promise in going for punchlines.
However, I think far more often The Daily Show is a continuing example of a better way to do things than simply breaking them into a left right binary. Even this joke, with its confusing metaphor of raisins and lawn mowers, points to a desire to see past the traditional breakdown (whether or not the overall joke is this enlightened, I'm not sure).
That's why I take particular issue with the line "But we're never going to get to that so long as opinion leaders like Stewart continue to take every cheap shot that comes their way." Claiming that Stewart and The Daily Show "continue" to take "every" cheap shot is not only false, it's not even supported by this article. The Daily Show falls short sometimes, yes, and that's why articles like this are a good way to keep them trying to live up to their own potential, but to claim that thye continually go for the lowest common denominator is so false it makes the truth of the rest of the article seem suspect.