Wrong answer, Microsoft.
There are advanced users of machines - especially these ASUS workhorses - that can not enable secure boot. You stated yourself that if we have custom drivers that it has to be disabled. Many of use boot multiple operating systems, some of which (Win 7, for example) don't support Secure Boot.
This is purely an operating system generated error. Telling us to break our hardware to get rid of it is not the correct solution. Provide us with a patch to disable this watermark, if not the check altogether. Just because we're running 8.1 Pro doesn't mean it's our only option - stupid stuff like this keeps up, and I will not be using Windows at all. I don't need it, I've just invested too much money and time into learning Windows 8 and don't want to put that experience to waste.