Just trying out ZPM at the moment and noticed that Flash, Java and a couple of other products get two different options for patching e.g.

Oracle Java JRE 1.7.0_25 for Windows (Full/Upgrade) (All Languages) (See Notes)
Oracle Java JRE 1.7.0_25 for Windows (Update) (All Languages) (See Notes)

The notes don't give much away in terms of advantages of using one over the other. Logic suggests that the Full package will install the plugin if nothing is there (or update if old version is installed) and Update will only patch if an older version is present - am I thinking along the right lines?