Interesting idea, but I think it ignores the fact that languages aren't equal. You may be able to save on hardware with gwan, but there's also the fact that writing your webapp in C could take a lot more time and effort than, say, php, ruby, python, javascript, etc. Even if the language itself isn't necessarily better, the available libraries are likely more complete in a language more often used for the web.
(Yes, I noticed that the authors seem to think C is the best language, but they certainly haven't proved it. YMMV, I guess.)