It's also an hedge against someone deciding they want a 4G Android phone, a BlackBerry, a Kindle Fire, a Windows 8 tablet or whatever comes along next week in addition to their other Apple devices. This provides another incentive not to mix and match.
Or an incentive to stick with Dropbox if you think you might want a heterodox solution.
Or an incentive to stick with Dropbox if you think you might want a heterodox solution.