Is it possible to use the application without connecting to a Standard File server? The page mentions the ability to use Dropbox "for added redundancy and peace of mind". But is it possible to use Dropbox as the only storage point? I would prefer to use Dropbox over their server or hosting my own.

It seems to me the applications act as clients that allow you to interact with your data. If so, why should it matter where the data is being fetched/stored? Why is it necessary to interact with a Standard File server?