Apple was an early adopter in this regard, but the standard is openly documented, and most recent x86-64 operating systems, including Linux and Windows 7, have support for it, even if it's not always used by default.

The last thing I remember Apple doing that could be remotely construed as "locking down" a Mac was when they still used a proprietary/undocumented memory controller, but that hasn't been an issue in many (10-15?) years. They stopped doing that long before they even moved off of PowerPC chips in 2006.

Thinking there's anything remotely nefarious here is very closely akin to arguing that any breaking of backwards compatibility is evil. This is just a new platform -- albeit one using the same instruction set as an existing one, and extremely easy to port to. It really isn't Apple's responsibility to ensure legacy operating systems they don't control support this new, documented platform.