nicola, my reasoning is simply that, in theory, I don't see any logic to the use of Dr in academia.
Of course, the world being what it is, I use it to annoy patronizing salesmen with 'Is it Miss or Mrs' questions, and of course I get a little jolt of pride thinking 'ooh! I'm Dr DeMontbaston, wow, how exciting' (cos I am newly Dr'd).
But, if we could manage to change conventions such that titles weren't used, I wouldn't need it for the first, and I am sure there would be some other detail that would keep reminding me how proud I was of my hard work.
After all, if we were all in Germany, we'd all no doubt be seeing newly-qualified professionals of all kinds experiencing the same sense of pride when they looked at their brand-new titles. But we're not used to becoming Architect DeMontbaston, or Engineer DeMontbaston or whatever, so we never miss it.
It's purely conventional.