Last time I looked, the proprietary bootloader for the Pi also had a license forbidding you from running it on boards not supplied by the Raspberry Pi Foundation.
That is true, for Broadcom's proprietary BOOTCODE.BIN, the (ThreadX-based) START.ELF VPU-side microkernel and their user-space graphics driver components which talk to it via the Linux kernel shims. (Although, note: you won't get a BCM2836 anywhere else anyway.) Broadcom do, however, have someone writing an open firmware I understand - definitely an unfamiliar world for them, so let's give them time and see what happens.
I am also aware of a complete reverse-engineering effort (for the purposes of interoperability), and that is all I'm going to say about that right now. :)
