Some of the issues that you raise are certainly valid, but with a slightly different slant can come out in a completely different light. I am not trying to skirt the issues you raise, just trying to put them in context circa the timeframe you were working in. My comments below.
All vendors deliver all commands.
Your conclusion is flawed, sorry. Even though a quick survery might actually substantiate your statement, that is not because of lack of interoperability. It is because of purchasing habits, vendor relationships, etc. In any event, most cells ARE in fact mixed because they have MS clients and Unix servers. The folks from Gradient, Digital and Dascom that listen to this list can verify this.