Quality matters, but there are other things that also matter, such as actually getting working code written. Some of us (and I've personally struggled with this for a long time) have a hard time letting go of our quest for perfection and settling for shipping code that's imperfect but works. When Jeff says that "quality just doesn't matter that much," what I took this to mean is: quality matters, but it matters less than we sometimes feel like it does. And that doesn't mean he's condoning writing crappy code; he's simply saying that we tend to overvalue this abstract concept of quality and that can have a crippling effect on our productivity.
Joel focuses on dogmatic adherence to development methodologies/principles as an example, specifically testing. I got the impression that he thinks testing is great and it has its place in the software development ecosystem. It tends to increase software quality and there are certain types of software for which it is really, really important (Jeff mentions framework code as an example). That said, taken to an extreme, testing can get in the way of getting things done... getting working code written and out the door / live on the server / whatever. It can also get in the way of modifying working code, as intentional changes to the way that code works always breaks some percentage of your unit tests, just as a regression will. And while catching unintentional regressions is great (and one of the best reasons you should unit test), constantly having to rewrite your tests every time you change the behavior of an internal class can be a real drag on your productivity. And that can be bad.
The key is to avoid being overly dogmatic in your adherence to development principles. Instead, be pragmatic and find a balance. Test enough to ensure adequate quality (whatever that happens to be for your product), but no more. Otherwise you're just doing yourself (or your employer) a disservice.