I been watching and thinking a bit about this exchange particularly, since I had a paper accepted in "Unix in Europe: between innovation, diffusion and heritage" Symposium which  touches on this topic.   I think it is really gets to the core of the problem that UNIX was caught with and I certainly did not understand at the time.

The issue here is were are all technologist and as such, we think in terms of the technology and often forget that its the economics that is the long pole in the tent.  Simply, computers are purchased as a tool to help to solve problems for people.  And the question remains who controls the money being spend. 

UNIX was written originally by a group of people for themselves.  The problem that they were solving, was how to build better programs and systems for those programs. Vendors, particularly hardware centric vendors, really only care that you buy their (HW) product which is where they make their money.   As it turns out applications software vendors, don't care about operating systems - as we used to say Larry Ellison never cared for VMS, UNIX, Solaris, or MVS, he cared how many copies of Oracle's DB he sold.

So UNIX comes on the scene and strange thing happens.   First AT&T is required by 1956 consent decree to make the IP available, they have processes and procedures to do so, so they do.  So in the 70s certainly, when the HW delivery platform for UNIX is a DEC, the people that want it are the same type of people that it was originally written -- programmers.

UNIX is a hit.... by the 80s and 90s, now we have two different group of peoples working with UNIX.   As Steve and Larry point out, those same type of developers that originally had used UNIX in the first place [which was cool... I'm one of them too].    The problem was the economics started getting driven by a different group, the people that did not care - it was purely a means to get a job done (we the programmers lost control of the tiger in return for a lot of money to start to develop the systems). 

As Larry pointed, most of the care takers of the second class of UNIX customer, did not give a hoot about the programmers or many of the 'norms' from the previous world.   Sun, Masscomp and eventually DEC did make SunOS, RTU, and Ultrix sources available to university customers (IBM may have also I'm not sure), but the hoops to get it could be painful; because they did not really understand that customer base as Steve pointed out (which turns out to have been an undoing).

But that was the issue.   Sun was able too see that trying to help the programmer was a good thing, but in the end, they could not sustain it either.  In the end, they got sucked in the same economics of cutting at deal with AT&T to create Solaris SVR4 etc.   Opposed Sun Forever, might have made it if they had actually make OSF 'Open Source' but they were too caught in fighting with each other.   Imagine if the Mach based OSF1/386 has been released, which was running before Linux with a window manager and you had IBM, DEC, HP, et al working to make it 'FOSS' - how different the world might have been.

But that would have gotten back to my point...  they made their money selling an application delivery vehicle.  They had liked to the control it, because it was easy to keep the customer if they did, but in the end, they really did not care.  

Now they have seeded the field to Linux and just left the OS to the SW developers and fallen back to what they really care about.   A place to run applications.

Clem