Perhaps the reason for "nobody writes tests" in the real-world isn't primarily because of time/cost, but because virtually no real potential bugs are testable. If you're writing a JPEG encoder or database model handler, yes, you can test that all day, but those things already exist and are well-tested for you. But if you're designing retail software or a web app, there are 2^10000 things that can go wrong, so most companies ignore automated unit testing in favor of human quality control.

This is all wrong. When you have enough people working on a codebase such that not everyone knows everything about it, tests are a great way to document the behavior. They're much better than something like a wiki, in fact, because nobody actually keeps that kind of documentation up to date.