@Vistapocalypse, If it counts, I have a Hyper-V VM that runs 2008 SP2, and MSE 4.10 - at the time of writing it still receives definition updates, but that might apply only to me - my local ISP has some kind of WSUS: I still can update XP/Vista without any 3rd party patches. I think that Microsoft Update servers are being redirected to ISP's network.
And you are right. A trick that is necessary to install it on Server 2008 / Server 2008 R2 - I had to run an installer with "mseinstall /disableoslimit" parameter. If it is not specified, I am given "OS is not supported" screen.