A lot of updates are like this, they do not do a real good job of explaining the things they correct. They seem to rely on people needing to know what they are doing, or in the usual case, install it if you don't know. When I first read this update, it sticks out to me (from my own experience) with SMB that you are then dealing with an in-network vulnerability. So, say some other system on your LAN sends a request to the unpatched system, then it could exploit whatever. BUT I do not know if you could fool Windows into responding to an SMB request through localhost, so then no other computers on the local network be needed.
Update catalog only shows this for Vista, 2008 and POSReady2009. That Embedded variation, not being that different from XP (it installs like Vista) then the "cry rivers" response is because there is no way to update XP x64... Or Server 2003 which would be more of a concern. SMB is available in SP1 at least.