mouse-over jokes

A few webcomics have bonus jokes in the title attribute of the image tag, meaning you don’t see the joke unless you hold the mouse over the image. These easter eggs necessitate new and glorious extensions just to make them work properly. Often the bonus joke isn’t all that great, but oh man, sometimes it’s funnier than the original punchline.

After discovering this trick in a webcomic I’ve been reading, I have to go back through the entire archives of a comic strip reading all the new jokes. Downside, or bonus?