Earlier quoted context omitted.
http://support.apple.com/kb/ht1948 Where's the problem?
Did you read the page you posted? The external USB device:- >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, th…
#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.