I said "there's significant pressure" -- that doesn't mean that companies don't sometimes overcome that pressure. One of my clients, who is a closed-source software vendor (surprise!), has allowed me to be involved in some of their code reviews which were very thorough. Like your experience, a pedant or two on the review committee helps make sure all the i's are dotted. It isn't that it can't work, it's that it often slips. In recent years, that client has migrated to a more informal code review process, relying more heavily on testing. I think the quality of some sections of their code has suffered thereby, although in general they've improved quality through more rigorous testing.