Dork Tower! One of the original successful webcomics is, surprisingly, still going! And still telling the same jokes!
John Kovalic’s continued success can be attributed to the fact that he was one of the first batch of successful webcomics. While the jokes are stale now, and even were then, it enjoyed the rush of popularity that came from the comic referencing things that nerds enjoy. There are many webcomics that manage to gain intense popularity relatively quickly thanks to this; XKCD, for instance, manages this with it’s maths, physics and web references. Questionable Content did it with indie bands (though has moved more into the exploration of the lives of it’s clone cast). It works in many arenas and allows for a mediocre joke to soar with a particular target audience.
While not a terrible thing in itself the key to referential humour is making the joke more than just a reference, it has to do something substantial with it and this is where many comics fall down.
Sound a bit hypocritical to you? Well just think how much more qualified that makes me to comment.