Mikuro, the test is not going to work for everyone, but it does test the browser's implementation of the standards.
It makes perfect sense for a developer to aim to pass these tests, though it should realistically be no concern of the end-user. The site won't work for some people, even in a compliant browser, as you have said. The point is, though, that the rendering engine is now compliant to the rules. You're forcing the engine to break that page by setting your font size to a minimum, which is OK, because no site is going to use such complex code to produce images in practice. It just means that Safari definitely follows the appropriate guidelines when it comes to comments, anti-aliasing, strict compliance to nested inline elements, etc. etc., which make NORMAL sites render as expected.