I want to think it isn't about that, but rather about removing the penalty you suffer due to level difference when trying to do content in ilvl117 or lower gear since you get penalized twice as a new or returning player. Once due to the stats on the gear itself and then again due to the extra 2+ lvl difference.
So if they made it so your ilvl would remain 119 regardless of gear once you completed the quests then you could focus exclusively on the stats in the gear itself instead of worrying about losing a few ilevels anytime you macroed a lower level piece of equipment or weapon.
PS > That was my main problem with ilvl gear when it was first introduced, since the moment you increased the ilvl of new items most of the lower level pieces you had became instantly obsolete, completely removing any sense of accomplishment in favor of the power creep gear treadmill.