>Contains an installation of Mac OS X 10.4.5 or later, or Mac OS X 10.5 or later, which is compatible with (or shipped with) the Mac that the USB device is connected to.
That's not Linux. Linux will not work with that method. Don't take my word for it; try it yourself, or ask Apple, or have a quick search of the "support" communities. See, for an example, this question on stack exchange: (http://superuser.com/q/27794/93703)
#1: You've moved the goalpost. You "asked" how to boot a Mac from a USB stick, not for instructions on creating a bootable USB stick to boot an operating system not specifically intended to boot on a Mac.
#2: That a particular kind of computer has certain requirements for booting that are not, by default, met by certain operating systems, has nothing to do with freedoms. The requirements aren't hidden, they're publicly documented, and can be easily accommodated by those operating systems if their developers desire.
From my perspective, it seems like you're arguing that Apple restricts freedom because it doesn't follow 80s-era "standards" for partitioning and booting, but instead follows the newer EFI/GUID schemes. I find such a stance more amusing and ironic than credible, particularly considering Intel is largely responsible for both.
You're right! I missed out 'linux' from "boot from USB". Sorry, I should have included that. Still, the point stands; booting Linux from USB is hard and not clearly documented anywhere and is tricky to explain to people. Maybe that's as designed, but there are so many of these design decisions that lock down the system to whatever Apple wants. And that jars with the "Think Different" sloganeering.
I truly, honestly feel like you're fundamentally misunderstanding what has happened here. Apple made a technical decision to follow the newer partition table, booting, and "BIOS" (EFI) standards from Intel rather than continue to use the legacy systems from the 80s.
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.
You've just managed to give the wrong information to someone, and call them stupid at the same time.