Could be some of the optional updates are actually update bundles/Service Packs and already include the important ones (mainly seen with .NET SP or IE including their precondition packages). Or they could have installed later versions of the same files (LDR vs. GDR?), making the first updates obsolete. Exmple: You have .NET 3.5 installed and a critical security update is listed on WU. If you now install .NET SP1 from the optional updates it includes the former. Thus the security update vanishes from WU. Second example: There are various security updates for IE9 listed on WU. If you now install the IE10 packages the IE9 updates are gone.
Thx for your reply! But then its hard to know whish updates i only need :/ or it is best to pick them all when to make a updated windows 7?