You forget to mention that secure boot can be disabled. And that there are Linux distributions that can handle secure boot.

To quote the Linux Foundation: "Linux and other open operating systems will be able to take advantage of secure boot if it is implemented properly in the hardware. This document is intended to describe how the UEFI secure boot specification can be implemented to interoperate well with open systems and to avoid adversely affecting the rights of the owners of those systems while providing compliance with proprietary software vendors' requirements." http://www.linuxfoundation.org/publications/making-uefi-secu...