I don't understand how anyone can develop software with myriad moving pieces without isolating and testing each component as it is written. It's like trying to figure out why your car won't start by sitting in the driver's seat and pushing buttons. I wouldn't ever presume to tell someone else how to do their job, but I can't imagine doing it any other way. (I prefer to write out my spec in BDD style, and unit test when the logic gets hairy).
I work at a development firm that mostly services local corporations, and the average time we have to maintain the software we build is fairly low. My boss and I both appreciate the TDD philosophy, but when client budget constraints are what they are, TDD is one of the first things to go out the window. Our CEO has (understandably) a hard time selling a project for 20% more money when the client won't get 20% more features. Additionally, if/when bugs come up, we're able to sell support and enhancement sprints. So really, TDD would reduce the (already small) revenue stream we get from support, at the benefit of being "one of the cool kids".
