My theory is that they are comedians that want to do jokes about the news and politics, but they find they must do extensive setups in order for people to get the jokes. This is a cause of deep misgiving in both programs as well. I bet if you asked them both, they'd rather the audience be informed enough to allow them to just do the jokes.
I love to laugh at them (and The Onion as well, OMFG), but there's a indictment of American culture lurking beneath both programs (more overtly done in The Colbert Report). And their greater success is in skewering the very presentational style of all televised news, giving their core audience a healthy dose of skepticism about how they get their information.
Thus making them all True American Heroes.