Illiterates' Entrance

I started reading "Eats, Shoots and Leaves" (the bestselling punctuation screed by Lynne Truss) this morning. I was trucking along quite nicely--so far, the book is really funny, while at the same time making its point--when I hit page 24 and almost decided to put the book down and stop reading.

Why?

I have two cartoons I treasure... The second shows a bunch of vague, stupid-looking people standing outside a building, and behind them a big sign that says "Illiterates' Entrance". And do you want to know the awful truth? In the original drawing, it said, "Illiterate's Entrance", so I changed it. Painted correction fluid over the wrong apostrophe; inserted the right one. Yes, some of us were born to be punctuation vigilantes.

Doesn't it make it funnier to have the incorrectly-punctuated version? I suppose that the whole point of the cartoon--and it sounds like "The Far Side"--is that there's even a sign for illiterates in the first place. But the fact that there's a sign and it's wrong has to be intentional, don't you think?

In the end, there's enough ambiguity in the situation that I'm not going to resign in disgust.