After examining the script inside the system updates, I found that this is a result of the security fix having created a "softwareupdate" program in /usr/sbin/. The system updates for 10.1.3 and greater detects its presence and then would refuse to proceed. A way around this limitation it is to rename softwareupdate momentarily to something else (say "lala") in the terminal program via:
% sudo mv /usr/sbin/softwareupdate /usr/sbin/lalaand then run the installer. Afterward, don't forget to switch it back, so that you can use 'softwareupdate' from the command line, as described in this hint.
[Editor's note: It was my understanding that previous updates were being updated to reflect the new secure update mechanism. At some point in the near future, they should be able to install without renaming the 'softwareupdate' application.]

