Yuhong Bao for some reason lamented that there is no 32-bit version of Windows Server 2008 R2.
Why would anybody want a 32-bit version of a server product? You would run into address space limitations right off the bat. you couldn't use it as an Exchange server, your Terminal Server couldn't support more than 100 or so users, your file server disk cache can't get more than 2GB (and probably much less), your SQL Server will be forced into AWE mode and even then, AWE memory is used only for database page caches, not for anything else.
Basically, a 32-bit server would be pretty much useless for anything it would be asked to do in its mission as a server.
(Device driver compatibility is a much less significant issue for servers, because servers rarely run on exotic hardware. Indeed, servers typically run on the most boring hardware imaginable and explicitly run the lamest video driver available. You don't want to take the risk that a fancy video card's fancy video driver is going to have a bug that crashes your server, and besides, nobody is sitting at the server console anyway—all the administration is done remotely.)