I'll put in my guess as to why the spec changed.
The ATF and friction modifier combination was cheaper and got the job done, but maybe not the absolute best performing option.
However, in order to save money due to volume Ford used the cheaper but acceptable solution. It would make sense that they would want their spec to be the same as production. If they spec'ed one fluid and used something cheaper, that would have looked bad.
So, once they were no longer using this "cost reduction", they changed the spec to the better solution.
