On the more reflective side: I think a lot of us have resorted to toilet humor because of the 75 word limit. Most subtle jokes need more background if they are to communicate. We are reduced to those jokes more slap stick in nature, (Puns, toilet humor, the farmer's daughter, etc.) which tickle our more basic nature.
Case in point: My backup story involved a Brachiosaurus and a T-Rex having a 'your mommas so fat' competition. But just setting up the competition, the two dinos, and a sci fi setting took me to sixty eight words: There was no room for a story as such.