This is because, as he has said before, his comic can be funny and interesting for people who have next to no D&D background. For me, the D&D references that filled the first 40 comics or so were fun, but only because I was just learning about D&D at the time. It was more funny because I got the reference than because the joke was... a joke.
Now, while I still appreciate the odd reference here and there, it's the characters and story that interest me. I'd rather have a three-dimensional character that I can understand and (in some cases) empathize with than a purely two-dimensional character cover the intricacies of D&D rules humorously for several (going on 8 or 9?) years.
Also, there are only so many times you can make the "Hey, isn't this rule weird?" joke, and that number is nowhere near as high as 829.
Edit: Typo.