Ever since the agents were upgraded to Windows 7/Windows 2008 the list of Windows updates (KB....) within the Inventory > Operating System > System Updates on some of them is empty or the tree is not listed at all.
Previously the list of Windows Updates was obtained from the registry key HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\HotFix
With the introduction of Windows 7 and Windows 2008, this has changed.
The list is now obtained by running 'wmic qfe list full'
On some PCs this returns an empty list: "No instances availabe" although Windows updates have been applied.
This is described in more detail in:
The described solution, http://support.microsoft.com/kb/947821, takes care of the problem with the wmic command and will also cause the System
Updates to show up after the next AM agent run.