Why does Windows Automatic Updates ignore SQL Server service Packs?
Windows Server 2003 Standard X64 Service Pack 2
No WSUS server in the picture just Automatic Updates enabled.
Default install of SQL Server 2005 Standard and Automatic Updates won't display Service Packs for SQL Server. It shows all kinds of other critical security updates for the OS, IE, etc...
I know this sounds terribly obvious - but are you using Microsoft Update, or Windows Update? If the latter, you need to enable the Microsoft Update feature that checks for all MS products, not just integral OS components (like IE)
The service packs didn't show up via the web update page until after I installed the .net frame work updates. Once I did these and rebooted SP3 appeared.