I'm not sure what My Uninstaller does, buy I'd guess that it does the same thing, because that's really easy, and more or less the only thing that *can* be done. From Windows 2000 (I believe, didn't bother looking it up at MSDN) the change-date (and only the change-date) was recorded for registry-entries. As such, it is very easy to get this information, compared to what it would take to find the actual install-date...
Update: Yup, it does the same thing...