I don't think there is that much room for minification in HTML: You can remove white spaces and line breaks, but essentially, that's about it without actually getting into the page's structure.
JS minification can shorten variable and function names, probably the biggest net profit in terms of saved space. With its fixed set of tags, HTML does not provide that possibility.
The option of gzipping HTML probably eliminates much of the need to minify anyway, especially as it is usually enabled for HTML, while it (unnecessarily) not always is for the CSS and JS file types.
