I think for those writing a technical book, myself included, just don't know if it's worth going self-publish with a minimal cut from payment providers and such. Or getting on board with PragProg who would help with marketing, editing, etc and still get a decent royalty.

I understand there are no clear-cut rules to go by, but even a generic "If you don't have 10k email list, 50% of PragProgs sales will most likely be higher" might helper writers understand when to get help.