Makes a lot more sense now, damn the misinformation spread by the masses!
Basically, as it is now the DR will only be a risk if the taunts are used to exploit the 4 second fixate of taunt in a chain, rather than use taunt every 10 sec CD.
I also read a blue post sometime a while ago that they would only have the taunt DR mechanic applied to bosses that could be exploited by it, and not as a general rule as it was pre 3.3.
00.0 Taunt 1 lands, DR count 1, 18s DR timer started
10.0 Taunt 2 lands, DR count 2, 18s DR timer restarted
20.0 Taunt 3 lands, DR count 3, 18s DR timer restarted
***All taunts immune for the next 18s
38.0 Taunt 4 can now land, DR count 1, 18s DR timer started
***and so on.
So if you had your tanks taunting every 10 seconds, then Gormok could have gone immune in those days (after 3 successful taunts, or 30s into the fight--remember the first tanks holds for 10s before the first taunt).
EDIT: as a note, you can check the taunt guide I wrote for any testing done for this. A lot of it is listed in the posts more so than the OP, but the info is in the OP.
There is generally a lot of misinformation spread on taunt.