Tom Y; Regarding the relative similarities in speed and turf species and selection between the greens and fairways, you are no doubt correct, IMO.
(With the possible exception of the Old Course)
Joe; Of course, the supt. for Old Mac, Eric Johnson, and his colleague Ken Nice are the experts ('masters', if you will) regarding turf at Old Mac, as Ken grew it in and Eric has been fine tuning it for some months now. Those two deserve the kudos for the purity of the playing surfaces, and the overall phenomenal presentation of the course.
Regarding the 5th/10th green issue, in preparation for the championship and with a bit of consulting from Jim Urbina, the two greens, once mowed as one, lately have been mowed separately. If you stood on the turf between the two, you would not only see a slight difference in turf height and character between there and the greens, but you would also see the lines of white paint dots denoting the respective green edges.
As to why Mr. Mills received, or was forced into, a drop from #5, Ms. Dodd one day and in an almost identical situation, had to play her ball from where it lay on the 5th, as she was playing the 10th, I do not know. The rules and their interpretation, at least to the observer, are quizzical sometimes.
Best,
Tom