Why isn't Ubuntu One just a versioning system?

Concurrent versioning systems like Subversion, GIT or CVS seem more consistent and more efficient.
I think most of the problems with Ubuntu One would be simplified if there was a little "Commit" and "Update" button.

This would solve problems like:

1.The files are not uploaded when I want to:
  a) I edit a file, save it, shut down the computer before Ubuntu One starts sending the file (what's a 5-minute window).
  b) I go to another computer and my changes are not there.

2. The files are not updated when I want to:
  I get home and expect to continue working on one of my files. This computer starts updating... slowly. I must give it about 5 minutes to "warmup" and I can never be sure that my files have actually been updated.

3. Inefficiency:
  10:00am: I start the computer and let it update the files from the cloud at its own pace (see problem 2).
  10:11am: I open a file for editing.
  10:13am: I save my changes though I haven't finished working on it: Ubuntu One uploads my modified file.
  10:18am: I save the file again, just in case: Ubuntu One uploads my modified file.
  10:28am: I go afk. My program autosaves the file: Ubuntu One uploads my modified file.
  11:00am: I return, keep working, save and shutdown the system (see problem 1)
Bottomline: 3 unnecesary commits and a missing commit, the most important one.