I think TED is fascinating, but I don't think it's a replacement for a college education. I can't really speak about the other two because I have only heard of them, I don't have any first hand experience. I hear what you're saying, I think it would be great, but I'm just not convinced we are quite there yet. Thanks for the links, I'll have to look it to them over summer break.
I've taken quite a few Coursera courses. The higher-level CS and otherwise technical courses are mostly great, introductory courses are awful, and the humanities courses can be fun but aren't really a replacement for actual classes. It's a fine way to learn new topics in a field you're already pretty familiar with, but I don't think it could replace undergraduate programs for getting people to that point. That might sound more negative than I mean it to; I love Coursera, I think it's a great project, I just think it really only shines in the graduate-level classes for students that have already been through a traditional university, as an alternative to just diving into an unfamiliar corner of the literature.
TED is definitely more focused on breadth and variety of subject matter, as cW mentioned above, so in the respect of "higher-level education," it may not replace traditional colleges. Khan, however, offers multiple lectures of increasing difficulty on an increasingly wide range of topics, from Basic Addition to Differential Calculus to the art of the Baroque period, along with exercises for some topics. It's certainly lacking in some departments (notably, there are no Writing, Philosophy, or Foreign Language classes which are so prevalent in traditional institutions) and the experience is completely void of any personal and social interaction, but it's certainly a good model for things to come, as you said.