Why?

Because “Downloadify is a tiny JavaScript + Flash library that enables the generation and saving of files on the fly, in the browser, without server interaction.”

You can generate in the client side, with no server interaction files that can be saved on the user’s computer.

Think about this:

Downloadify, a clientside persistent storage script ( like persistjs or lawnchair), some manifest file for html5 cache  and of course a capable browser , and you have a full offline webapp capable of saving files to local disk and that can be syncronized with the server when internet is available.