Like I said, just from experience.... no documented evidence. The nikon ttl spanks my PTTL at every family event I attend. The Pttl is just not consistant. under exposes then really under exposes to the point that there is no consistant compensation I can use. My cousins D80 is just way more consistant. So much so, that if both cameras are there I will use hers every time. Now in natural light, forget me using the D80....
The Pttl flash is really the only think I have never trusted on my two pentax cameras. And if I had a nickel for everytime I heard "user error" about it, I could buy a Nikon System!
I do as you mention, get better results in manual... but at event with kids and varying conditions a consistant PTTL would be preferable!
Just my experience...