Technically, it does run offline. If you pop open your developer console, you'll notice it isn't making any requests. All of the wallet generation is done on client side, no public address or private key ever touches our server. After the page loads, it'll still work with no internet connection.
I think both IE and Firefox has an "all in one" archive format for a webpage that includes all the external files and can run directly from the single file.
That would be a neat alternative.
But I think they built a website for the traffic, not to give away their work.
