If a Sony product happens to have a fake FTDI chip in it, this is FTDI's way of incentivizing Sony (via angry customers) to manage their supply chain, because as you say there's an incentive even for Sony to cut costs where they can- perhaps by turning a blind eye when they get some suspicious batches of chips for a great price, and claiming ignorance later...
Everyone, in demanding the lowest price no matter what (all the way up the supply chain) bears part of the blame.
We are of course witnessing a visceral response on the part of HN voters reacting to my comment, who are exemplifying why this is a hard problem to tackle. It isn't MY responsibility!