I noticed in 10.3's Software Update that it gives you the option of updating and saving the package under the Update menu. Before under 10.2.x it used to ask if you wanted to dl the update to the desktop to keep the file for later use. 10.3 nicely puts the package (10.3.1 in this case) into a folder called Packages (located @ Library/Packages). It nicely shows you the package in it's location after the install to show you where its at. This is the first time I noticed this and apologize if others have posted this before
-Jerry C.