But Apple isn't having any of it... They are hosing apps that use Dropbox' SDK, because if your phone doesn't have Dropbox, the Dropbox code pushes the user to the Dropbox site to purchase storage, circumventing Apple's rule about in-app purchasing.

Dropbox is already in a tough niche, and decisions like this ain't too bright....

http://www.pcpro.co.uk/news/enterprise/374440/apple-blocks-dropbox-based-apps