Earlier quoted context omitted.
"Microsoft has SkyDrive, integrated with Windows and WinPhone. Apple has iCloud, integrated with OS X and with iOS. Clearly you can see a pattern." This is exactly the case for staying with Dropbox. Otherwise, your cloud provider has more leverage to lock you into their products. Dropbox is motivated to support multiple platforms.
For what it's worth, SkyDrive has sync engines on both Windows and Mac while having apps + auto picture upload on Android, iPhone and of course Windows Phone.
I mean, skipping over Linux users that are a significant chunk of the market if you ask me, but lets assume for a moment that Linux home users don't pay much for their software or whatever. What about governments that have adopted Linux? What about Linux being the most popular OS for servers? What about Linux being used in the educational system, like with Raspberry Pi?
And even for yourself, lets say that you'd want to do your own backups of your Skydrive or Google Drive and so you quickly setup your own home Linux box that should synchronize your account. Surprise - you're not important enough.
This is platform lock-in, pure and simple. Microsoft is no better than Google. Don't get me started on Skype ;-)