The difference isn't just replacing {} with <>. Notice that the tag name is only specified once. The end tag is only an end } not a </tag>. This is more satisfying to programmers because the SGML style allows mixups like <a><b>text</a></b>.
I'm not sure if expecting the programmer to know all HTML tags but not how they are used is the right way to go :P
Either you say "ok, i want to get rid of HTML and make it really easy to build a website" or not. This approach is neither, in my opinion.
In my opinion, that's a problem of most of those "fancy" markup languages. Why should i bother using this (or haml for that matter), if it only adds another layer of complexity and yet another "language" to learn (for me and far more important for every other person that may join a project in the future)? It may look prettier but it introduces overhead and potential other problems. Is it worth it? For me, it's not.
