The point being that as long as there are external files (css,images,etc) in the page you will have to save it as 'Webpage (complete)' (or the equivalent in your browser) which saves the HTML file and creates a directory for the external files. If you are saving a bunch of sites/pages this way you end up with <i>a lot</i> of directory/html-file pairs. And were you to ever move these around, you would need to make sure that the directory/file pair moved together. It makes much more sense to have it all in one file (and as with MAFF a file that doesn't necessarily need a browser to extract the contents).<p>Linking to this to the subject matter, most of the lessons have to do with math and science, in a way that requires diagrams and specific notations. Both of which cannot be represented in plain-text or HTML without external files.