I was only slightly connected with the development of the POSIX standard,
and as has been mentioned here, AT&T was a full participant.
The real conflicts were in a related area and at the time were termed The
GUI Wars. Basically, it was AT&T and Sun pushing OpenLook and everyone else
pushing Motif. I seem to recall that the Motif folks (Open Software
Foundation) more or less forced IEEE to just accept Motif as a standard.
I was on a different committee that was trying to standardize a universal
GUI interface that could work on any GUI, including Mac, Windows, Motif,
and OpenLook. My product, XVT, was the base document. We never got past the
draft stage.
Marc