I suspect Sun just wants to maintain face time with clients, but here's another opinion:
"Sun recently announced it would open-source its Solaris operating system. While declining to get specific about timetables and the type of open-source license the company plans to use, John Loiacono, executive vice president of Sun's software group, promised that Sun will "be very aggressive and progressive in our approach." For now, all we can do is speculate.
There is a widely held assumption that Sun's motivation is to emulate the Linux phenomenon with Solaris. If we apply the computer-science principles of emulation to this announcement, the license (once it is available) will provide considerable hints as to where Sun is going.
...While we can only speculate about Sun's motivations, it is fair to point out that emulation is a sign of respect. We emulate mentors, teachers or role models. Imitation, on the other hand, is a sign of flattery. We imitate rivals or competitors. Perhaps, in the long run, this distinction will provide all the insight we need into Sun's decision."