The metrics that show unit testing leading to better code are based on comparing unit testing to no testing, never comparing unit testing to actual blackbox testing.
The point of my article was that testing is a component of software development, it is not the feature attraction. Good developers test their work before handing it over to QA, not the bullshit you have doubtless heard that we didn't test at all.
And the reason the emphasis has shifted to testing is that most of you kids have grown up with channel-surfing and games and never learned to concentrate, and work under conditions where concentration is unachievable because of interruptions. So you write buggy code and try to make up for it by writing tests.