One thing that video has that HTML doesn't: single-file archive ability. Sure you can have a single HTML file as long as you keep it text-only, but most of these topics are going to be diagram (and math figure) heavy. There's just no good way to archive the content for later perusal. (Granted YouTube doesn't want you to directly download the videos, but it's not like it's that hard to circumvent -- and once you have the video you can easily find a player for it on any platform)<p>[Note: I don't count .webarchive or .mht files as 'good enough'. .webarchive files are Safari-only, and I don't even know of a tool to be able to extract data from them. .mht files are 'sorta' supported (IE, Opera, Firefox w/ an extension), but I don't like the idea that the data is Base64/MIME-encoded. Personally I like .maff (Mozilla Archive File Format). It's only supported in Firefox with an extension (and nowhere else unfortunately), but it's basically a Zip file with the HTML/CSS/images inside of it.]