Would respectfully disagree. Dropbox and Box are building an awesome app platform as well and as long as users want neutral solutions (non iOS or Windows), they should be OK. In fact Box and Dropbox will start specializing as the author noted.
iCloud is useless at work, and my officemate has switched from SkyDrive to Dropbox for the same reasons. We now both doubly benefit from the wide-ranging accessability and sharability of Dropbox.
Basically I don't see a difference between dropbox and skydrive (or gdrive or....) as a developer, if I had to choose, I'd probably choose a platform from a company that has a long history of building platforms (Microsoft or Google or any other big co) as opposed to dropbox which is a tiny startup somewhere with no viable long term life expectancy.
Given these why would I choose a neutral API?