Is that CDE? Because everyone thought CDE was the bomb and it was a total pile of crap. I had to use that on an old Sun pizza box back in the day.
CUA seems to be more like a "this is how this stuff should operate" not an interface in and of itself. I'd rather read the cliff notes version than any IBM doc: http://en.wikipedia.org/wiki/Common_User_Access
Your slim pizza must have been one of those DEC Alpha cores capable of running Windows NT3. My company should never have sold our development unit, these are rare consoles which excited our best developers back then.
Up until the 1990s SAA was a standard that uniquely shaped and defined IBM systems thinking, which meant industry thinking. SAA wound up in most application UIs and OS shells, some more than others like Windows 3.x and OS/2 CUI, and the OSF/Motife/CDE/Gnome stream which you mention. The only holdouts on the entry desktop were Apple and a couple of UK firms which I forget.
As with any movement, the enforced standards and guidelines first made their appearance in fourth-generation development suites. In those days this meant big OS/360 packages monitored by CICS and character-based IDEs running on 327x concsoles, and mainframe developers were slowly encouraged/intimidated into eventually complying with IBM SAA guidelines. A lot of PC business and network software were designed to interoperate with or generate output for the big systems and naturally followed developments in the higher, IBM-dominated markets. Prior to this it was a user's nested mess of interfaces, a despairing situation for most non-techie users who faced retraining for every newly entrenched core suite. It was like the convoluted situation of varying Wordstar and Lotus and Ashton-Tate UI standards in the PC-DOS world, but with $million mainframe applications and utilities at stake, all fragmented in UI design according to each vendors' idea of how a console interface should be.