"Alt" or "Hover" Text works on one site in iOS (Safari); but not another

Greetings everyone.

I had to Google how to see hover text; then smacked myself on the forehead w/, “I knew that!” (but forgot).

Many cartoons, like XKCD have a second punchline embedded in the webpage’s coding, so viewers can get the second joke by hovering their cursor over the image.

To see the text in iOS, simply try to save the image and the text appears above the “Save Image” dialogue.

You can now see the alt-text in iOS 7’s Safari – reddit

This works on XKCD, but not on d20Monkey another webcomic.

(Sidenote: You’ll need to go to the beginning to see my favorite arcs; then get caught up w/ the author’s current experimentation(s) – Sorry for taking away about 4 hours of your time!)

I looked at the HTML and XKCD uses the “title” field to add the text and d20Monkey uses both the title and alt fields (repeating the text). That does not seem to work.

Anyone know why?

I’m more curious about how to make it work; but am also interested in some usability / interface design tips(!).