I just don't agree. It's not Muppet humor.
Think of it this way...
I could imagine the scene being just when they're forced to leave the theater after the tally's decimal point is realized. It's a somber realization, but Fozzie's still behind the stage trying to get those shoes off. Tex snarls at him, and a very dejected Kermit motions for Fozzie to leave. But as soon as he starts walking, a loud Whoopie Cushion sound is heard. An apologetic Fozzie raises his head in shame, a deafening silence fills the room... I'd imagine Hobo Joe would say "This is a bit too low class for Hobo Joe" (who then lets out a loud disgusting cough)... Tex freezes, everyone freezes and looks at Tex, who for the first time ever started to smirk, then snorts, and is the ONLY one in the theater who starts laughing thunderously. An annoyed Piggy says "THAT'S WHAT it took him to LAUGH?!? THAT?!?"
So the joke, how I see it, isn't so much "ooh! Hey, Fart!" but rather it took the stupidest and most juvenile thing in the world to get someone who never was able to laugh to break out. Of course, I don't see how that would have worked with the reveal being that they're supposed to walk out there, still depressed to millions of fair weather fans...
Still, the ending needed something, and I wonder if that would have bulked it up.