The point is that HTML is a standard format that many tools and people are familiar with. HAML is not. While HAML might be more succinct, there is a tradeoff being made that is probably not appropriate for all situations.
I can agree with that, I wouldn't use a code-based markup generator simply because I couldn't see how you'd add design-based containers and things in there. Seems to eb good at producing semantic content markup, but not for full pages.
