This doesn't prevent the OEMs from doing anything, it only prevents the end users from doing things. The OEM can have two versions of every tablet/phone they make, one that's Windows-certified with UEFI and another identical one that's not Windows-certified that they can offer with Android, Linux, or whatever. All this agreement says is that you can't sell Windows on a device that can be flashed with a different OS afterwards.

So this creates devices sold with Microsoft software that can only run Microsoft software. It does not stop anyone from selling devices with other operating systems, even the same manufacturers with identical hardware. Should Microsoft not be allowed to offer these computers? If consumers don't like it they can vote with their dollars and buy the Android/Ubuntu/WebOS tablet -- they just can't buy the Windows one then delete Windows and install Ubuntu.