And that's exactly what I didn't mean. It's a sample of one, and offers no information whatsoever about how much code quality can contribute to success, except that rubbish code doesn't totally preclude the hope that a product might be successful.

Let's say things had turned out a little differently, and someone had used one of those SQL injections to irreversibly erase all of early Facebook's data. We'd probably never have heard of it again.

Code quality is a good thing - like scalability, and security. Ultimately, you might succeed without it. But it'll probably be easier if you do.