Why aren’t all Microsoft Patches MSI Files?

I have Active Directory and install programs via Group Policy as MSI files - why aren't all of these updates available in MSI format - I suspect there is a technical reason, but was curious since the AD-group policy scheme works so well.

From the microsoft.public.softwareupdatesvcs newsgroup
Good question, and one that has come up many times before. The "patch management" solutions that are provided for each different piece of software from Microsoft is often distinct since each group developed its patching solution independently of other groups. There is now an effort going to reduce the different methods of patching different software. As for timescales and whether MSI is to become the standard is unknown at present.