This is one of those classic forks in the road.

If you make it cross platform, you make it easier to be a lingua franca of sharing between loosely connected people. Dropbox is handy for sharing project files between consultants and clients, for example.

OTOH, if you make it platform-specific, you can make it a better experience for people who use it to synchronize their own files or between closely connected people such as colleagues on a team that have a single standard OS.

The whole thing seems analogous to Apple’s strategy for integrating hardware and software. It sacrifices “interoperability” for just being better. I suspect a lot of the same arguments apply here.

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.

Yes, in the end either Apple will draw users into its "ecosystem" via iCloud, or it will remain a handy option for Mac-only users. Dropbox has filled a need for me (synching across multiple Apple devices) that Apple could easily expand to new areas by leverage the native OS.

Then it becomes an issue of trust – who is putting more skin in the game to protect my assets? Dropbox has always had a problem establishing trust for users like me who absolutely cannot afford any negligent gaffes like leaving my account open to accept any password for a few hours. On the other hand, Apple has a very short track-record as a manager of a big, shared data repository open to the general public.

Out of curiosity, are there people that require files synced over the internet across multiple devices maintain access control? I mean, is that a requirement that people actually have?