You've listed a lot of good reasons why open-source for business isn't used more frequently, and they're all consistent with my experience as well. Are you familiar with any consulting companies / vendors who DO advocate open-source solutions?
I've been considering starting a FOSS MSP / FOSS B2B consulting firm, but I've consistently come to the same conclusion that the tech industry and business culture here are almost innoculated against open-source. If you know any firms that DO recommend open-source solutions I'd love to check them out.