On the platform upon which Microsoft has a monopoly on operating systems, the standard mandates that users be able to install their own keys (and thus be able to use the secure channel) or else disable secure boot. Moreover, Microsoft is not dictating that OEMs preinstall only Microsoft's key, or indeed that they preinstall it at all. It's all very well shouting "monopoly!" given the undoubted advantage this gives Microsoft over other OS vendors, but the standard already offers sufficient concessions to said vendors that they are not being shut out of x86 entirely. It's difficult to see what a regulatory body could add to that.