I think you're misunderstanding what they're trying to say. I think they're trying to escape the perfectionism that can stall a project and halt progress. They

I think you're misunderstanding what they're trying to say. I think they're trying to escape the perfectionism that can stall a project and halt progress. They have a very extensive testing framework that tests for correctness. Even if they didn't, if a browser isn't doing something correct, people would notice right away. Their "we don't care" assumes people working on the project are competent and will produce code that is good enough™. Modern WebKit browsers tend to be extremely stable, enjoys a clean code base, and very fast, so they're doing something right.