Upgrading MODx Installs via SVN

Is there any reason that this would not also work with MODx?

http://codex.wordpress.org/Installing/Updating_WordPress_with_Subversion

None, yet¹.

I actually maintain a few sites this way, and even use it to keep local modifications merged more easily.

¹ - In the future, this may be a little more complex, though not impossible, simply because all of the local subdirectories (assets/, manager/, etc.) in MODx will become configurable individually; so your local deployment may not match the SVN directory structure.