Modern "Jobsified", "New World" Apple hardware is in essence just about as "closed" as, say, a Teron board...
I was under the impression that BeOS ran into the "no documentation for you" issue and that's one of the reasons it tried to move to x86. Not so much that Apple locked them out via a closed BIOS but more that they did not provide any documentation. Not sure how the flash-upgradable current BIOS helps with anything... unless you're trying to say that there are better sources/documents for Apple hardware now?