When I did my first greenfield TDD project, I was utterly amazed by the low defect rate (3 in a year, only one really related to coding) we achieved with a fairly relaxed attitude towards comprehensive code coverage and edge cases.
This seems to be related to a slightly different observation, which is that most of the really awful/pernicious bugs tend to be super simple/stupid once you have found them. You know, the "slap your forehead" type of bugs that you just couldn't see because they were too obvious.
My suspicion was that firing even a few monte-carlo rays into that potentially huge state/argument space is sufficient to induce writing the correct code in the vast majority of cases, it's great to see pretty convincing empirical evidence for it (rather than just anecdotal).
Of course, we all "know" that testing is insufficient, after all Dijkstra said so. Did I mention I love the name "This will never work in theory"?