Actually, I see this one as a sort of transition book in the series. We have seen Discworld and, in particular, Ankh-Morpork, develop through the series. We gone from Medieval to Regency to Industrial Revolution and Victorian. Cohen and co. are part of an outdated era on Discworld.
They don't fit into the books any more so this is Terry's way of letting them, literally, go out with a bang. I think the books have moved even further into a more modern era since this book.
Which takes me back to favourite illustrations.
Mine is actually two - it's sort of the Before and After pictures of the minstrel. That picture of him in rags sitting on the rock playing his homemade lyre is excellent in my opinion.
"Goodness is about what you do. Not what you pray to."