Hardware manufacturers can still give users the option of disabling secure boot and running any operating system they wish.

Concerns were raised that secure boot could prevent or hinder the use of alternate operating systems such as Linux.

Advantage of this system is secure boot, which is protection against viruses.

But the prohibition on disabling secure boot does place another obstacle in the way.

Seems they could still release tablets with the ability to disable secure boot if they wanted to.

Might want to add something on Windows 8 Arm computers being prohibited from disabling secure boot.

Is there any evidence that it does circumvent secure boot?

The referenced links don't mention secure boot at all, just Windows 8.

Other developers raised concerns about the legal and practical issues of implementing support for secure boot on Linux systems in general.

Several major Linux distributions have developed different implementations for secure boot.