I don't, just like you don't know it's not true. It's my opinion, based on what I see at friend's homes, my family and relative's homes, and so on. NO ONE I know uses custom guides (including myself). I did set them up on a receiver a long time ago (mainly a guide for me that filtered things like the Nick channels, Disney, etc as well as a "kid's" version that only included kid-friendly channels) but no one used them.
Just because people here use them, like them, and want them, doesn't make it mainstream. People here are power users, TV geeks (I'm a geek myself, albeit not a TV one, so I say that in a positive manner), and so on. Custom guides are something that Dish has offered for a very long time, so it may be "tradition" as much as anything. Since I don't use them, I can't confirm if it's still a problem, but for a long time, Hoppers (and Joeys, I presume) did not remember your guide selection. Wouldn't they fix that if it was important to a lot of customers ? These set-tops report, or can report, everything. Dish knows what people use and don't use and prioritize accordingly.