But why? He doesn't say that anywhere. He doesn't even lay down rules about how you should build any site. He's all about carrying out user testing. He suggests techniques that he thinks are likely to work, but he always qualifies these opinions.
What I find particularly irritating about Hank's blog post is that he seems to me to be saying "useit is ugly" rather more than he is saying "useit is unusable" - the latter if provable is relevant, but Jakob's articles are not about beauty - only usability.