As is probably well known, Microsoft spends a tremendous amount of time and resources on marketing and education both internally and externally. At times it seems as if only word of mouth and a few more people saying the same thing will drive the message home.
To that effect we'd just like to reiterate that indeed, Windows Server 2008 and Windows Vista Service Pack 1 are in fact the same code base now. This means that when you go to the System control panel, Windows will show Server 2008 RTM as having Service Pack 1 already included, this can be seen in the screen shot at left.
Now that servicing will be done against the same codebase, the first Service Pack for Server 2008 will be SP2.
The official statement can be found in KB 949607.