Apple's 'full' solution involves the necessary purchase of their hardware and software as well. Dropbox works across the board, without prejudice.
It's the same thing that happened with backups, they came up with Time Machine. Pretty much all the Mac users I know have a Time Machine backup.
I believe the same thing will happen with version control once Versions support is wide spread. Normal people will know about keeping versions of their work rather than multiple differently named files.
More than 45 million people use Dropbox. I think they have that part of the problem solved.
Does the Windows versions suck as much as iTunes? (including installing that pesky apple updater).
Going on-topic, I have a dropbox account but the 2 GB limit (which I managed to make 3.5GB after referring) is very limited. In addition they do not support WebDav.
I recently opened a free Box.net account and I am really happy with it. Because it has webdav support (box.net/dav) I can "mount" the disk in any computer as a drive (windows) or folder (linux).
I personally prefer this approach to the DropBox "replicate everything on each PC you enter". But I understand they are solutions to different issues.
The same was said about iTunes, but it eventually appeared there. It wouldn't surprise me if more aspects of iCloud eventually appear on Windows.