> The other thing is that don't products such
> as Solaris, AIX, and HP-UX belong to a
> second main branch of Unix that is based on
> the commercial ATT released code, while
> BSD is based on the BSD's release(s)?
Well, Solaris, AIX and HP-UX, as well as IRIX and a bunch of less relevant systems (such as Reliant) are based on AT&T Unix System V. Most of them licensed the code before SVR4 (Release 4), but when SVR4 was out, they all incorporated code from it into their systems as well. SVR4 is also what they're all licensing from SCO.
The free BSD systems today are based on 4.4BSD-Lite, which was the last release by Berkeley (in 1994). This release does not contain any AT&T files anymore.
> As such no BSD could ever even become
> Unix® under the current standards... even if
> they were going to pay.
No. While it is true that most UNIX-branded systems are System V derivatives, the code heritage has absolutely no relevance to the certification. The ONLY thing that matters is that you pass the tests which verify that your system supports ALL the interfaces and utilities defined by one of the SUS standards (the one you want to conform to) correctly. One of the systems I can think of that is not derived from System V is Tru64 UNIX (or before that, Digital UNIX), which is built on Mach (an early monolithic version of it I think) and BSD. Another is MVS or OS/390.
The current standard is UNIX03 or SUSv3, which was originally released in 2001 and amended in 2003. There's not a single system already conforming to it, however, so SUSv2 (or UNIX98) has more relevance for now:
http://www.opengroup.org/onlinepubs/007908799/