Activewin reports that Michael Howard mentions on his blog that recently MS had all the major OEMs on campus to discuss SDL (Security Development Lifecycle). MS asked the OEMs to enable DEP/NX in the BIOS by default on all their shipping PCs in time for Windows Vista.
The reason for this ask is pretty simple, for ASLR to be effective, DEP/NX must be enabled by default too.
Michael mentions that all the major OEMs (you know who they are) have agreed to not disable DEP/NX in their BIOSs by default.