I installed NIS 2010 back in September (2009) and it used to keep track of software installations. It doesn't do that any more. The last installation on my system according to the Performance window was on October 13, 2009 for the monthly Windows XP SP3 security updates. I can tell you that I've done a number of installs since then, including the November 2009 security updates. It still intermittently tracks software downloads, but not installations.
NIS 2010 simply stopped keeping track of or logging installs after October13, 2009. Is there any reason for this?