By the way, nice history of that joke pltrygyst, I wasn't familiar with Gregory.
And I do think Bill Maher probably did nothing to try and hide the fact that it wasn't his joke. Adams on the other hand is portraying PHB as trying to take credit. Saying Maher's name in the same sentence as Adams' isn't exactly fair by the way ;-). YMMV.
I didn't see this as "stealing a joke"...at least not where he's trying to take credit. I think the saying is well known enough, and he's just portraying the PHB as spewing cliches and idioms. The originality comes when Wally responds to this now cliched joke, turned training material...."If I work like a dead pig.....". Wally is twisting the simile to his advantage, in order to mock it.
Well, jtgd is close. The joke, explaining the difference between being involved and being committed, originated on Dick Gregory's 1961 album "In Living Black and White."
It followed one about the difference between the US and Israel -- "Here we have ham-and-eggeries that are fronts for bookie joints; in Israel, they have bookie joints that are fronts for ham-and-eggeries."
And the US and South Africa -- "At the battle of Bunker Hill, it was 'Don't fire until you see the whites of their eyes.' At the battle of Leopoldville, it was 'Don't fire until you see the whites.'"
Before he became purely political, Gregory was tremendously funny without losing his edge.
I'm a bit surprised that both Adams and Maher would steal this one without some attribution. I thought better of both.