About a few months ago, App.net decided that being a Twitter clone won't work, so it is trying to be a data framework that anyone can use. (Which incidentally Dropbox is also trying to do.)
That was always the core of their model. The idea was to monetize a Twitter-ish network by monetizing app development and API usage, a model which was allegedly on the table at Twitter itself at one point. They've just communicated really poorly about the whole thing.
Isn't DropBox's data api more granular (record-level). Where App.net is more coarse (file-level) and not really ideal for changing data. In fact App.net only has one primitive that you can edit and it can only store up to 8k of data.