I guess the main Reason for the change is that, indeed if you are very lucky (just ignore the % and think of the possibility) you could get 4 turns in Total without the change
Round 1 - Enemy Turn
Round 1 - Your Turn, you roll Triple 6
Extra Turn (now you wouldn't get an extra turn with the triple six but what happens next is
Round 2 - Roll initiative, if you win
Round 2 - Your Turn, you roll Triple 6
Extra Turn
Round 2 - Enemy Turn
Even if the odds are almost 0% for this to happen it still is possible and 4 Turns of you, in which the enemy can't do anything but cry is REALLY overpowered
This could Win a game by just 2 very lucky rolls