Yeah, I've got to keep going with @blwnsmoke
on this one.
I won't speculate on the engineering other than to say that the "true" fix is probably way, way too expensive to pull off. Hence, you get a solution that fixes a significant part of the problem, but not all of it.
Unfortunately, the game is "how much can you get away with," and that's not to speculate maliciousness on Ford's part as much as recognizing that life is a series of trade-offs. And every human and company will perform that analysis.
In my case the problem has been especially intermittent--I wonder if it's my fuel quality that's at the root of this, not that it gives me any comfort that "good" fuel wouldn't smell into the cabin. But I'm not an engineer, I'm not getting ill, and my CO detector thingy hasn't triggered either.