It is, not to put a fine point on it, an absolute asshole move.
They could have merely disabled the GUI element which enables the undervolting. This would've made it so you need tools like http://ruexe.blogspot.com/ to edit the EFI variable which firmly put it outside of the reach of the average consumer but still makes it possible. But no, the EFI variable is protected and unless you manage to break the firmware it's impossible to change it. Sigh.
They could have merely disabled the GUI element which enables the undervolting. This would've made it so you need tools like http://ruexe.blogspot.com/ to edit the EFI variable which firmly put it outside of the reach of the average consumer but still makes it possible. But no, the EFI variable is protected and unless you manage to break the firmware it's impossible to change it. Sigh.