I can respect this; I feel like some of the later books were a little weaker, but preserving his stories as his own still protects the series as a whole.
I still haven't been able to make myself read The Shepherd's Crown. I preordered it, I have it, but there's something about knowing that whenever I read it will be the last new Discworld thing ever that makes me keep waiting. I grew up with those books, and can still remember being all of 10 and a woman at a used bookstore handing me a copy of Wyrd Sisters and explaining that it was Very Funny. They may actually be the only series I enjoyed at that age that I never felt like I outgrew--even as an adult reading the Tiffany Aching stuff for the first time it never felt like pandering to kids.
Compare and contrast with, like, Xanth, which I think is the other fantasy series I started reading around then and which now seems like so much gross trash.