Excellent riposte! Mine was going to be somewhat less polite :-)
Can't stress enough that TDD is not about testing (sth. DHH, like many if not most critics gets wrong). It is about development and design. The fact that you get a pretty decent test suite out of it is a nice side effect. (Love me those side-effects, wouldn't want to program without 'em).
I also find that whenever I skimp, it always comes back to bite me. And usually it was because I hadn't understood the problem-space well enough to write a proper test. That's one important part of TDD for me: I have to understand the requirements well enough to actually write a test for them.
And the OP is also right in that Rails is a bad environment for TDD, as far as I can tell, because all the magic and auto-integration gets in the way and has to be laboriously stubbed/mocked etc.
Maybe it's time the community got over Rails. (See also Uncle Bob's excellent architecture talk: http://www.youtube.com/watch?v=WpkDN78P884 ).
