Well, likely VMO or some other client type application _was_ installed in the past, even if it's not there now. If you look in the registry I'll bet you find both Active Voice and Cisco branches under HKLM\Software\. The version check looks for one or the other (Connection uses the Cisco branch, Unity uses Active Voice) - if both are there is takes a shot in the dark.
On a clean Unity install you will not see the Cisco branch under normal circumstances - I tested this in the lab on 4.0(2) through 4.0(5) to be sure and it works fine so the only conclusion I can draw was at some point in the past there was something installed that stuck in the Cisco branch.
That said, I updated the version check to fill out full version info from both branches and make a more educated guess as to the validity of the local install (i.e. do files exist in the appropriate paths) instead of just relying on the registry key existence - it should handle it better. I didn't roll the version number, just repackaged the setup:
http://www.ciscounitytools.com/App_BulkEditUtility_40.htm
download that and install it over the version you have and see if it gets the proper version info for you.
