One area to be careful is there can be different compatibility between the updates, for example I have seen many updates compatible with Windows XP, Vista and Windows 7 to be superceded by an update only compatible with Windows 7.
Here is what Microsoft says:
"WSUS does not automatically decline superseded updates, and it is recommended that you do not assume that superseded updates should be declined in favor of the new, superseding update. Before declining a superseded update, make sure that it is no longer needed by any of your client computers.
The following are examples of scenarios in which you might need to install a superseded update:
" If a superseding update supports only newer versions of an operating system, and some of your client computers run earlier versions of the operating system.
" If a superseding update has more restricted applicability than the update it supersedes, which would make it inappropriate for some client computers.
" If an update no longer supersedes a previously released update because of new changes. It is possible that through changes at each release, an update no longer supersedes an update it previously superseded in an earlier version. In this scenario, you will still see a message about the superseded update, even though the update that supersedes it has been replaced by an update that does not."
From: Microsoft Windows Server Update Services 3.0 SP1 Operations Guide
http://www.microsoft.com/en-us/download/details.aspx?id=4813
