Is the bigger news that Garfield got a ball up his rump... or that the pink carpet from last week is back? I don't know if other comic strips think an acceptable Sunday visual gag is a ball going up a cat's butt, but my guess is not.
In his book In Dog Years I'd Be Dead, Jim Davis explains that he tries to make the Sunday strips more visual and broad in their humor than the more dialogue-oriented daily strips. I guess stuff going into Garfield's butt is pretty universal, but also universal is the question "why can't Garfield feel the ball with his feet?"
The answer: if the joke world operated exactly like the real world, nothing would ever be funny.
And cats and dogs wouldn't be walking around on their hind legs.