The idea is, as I see it, that upon reaching level 60, players are no longer rewarded for further gameplay time they accrue, despite there being a potentially infinite system in place for rewarding players in this way.
This concept is nothing new to the RPG experience, but is one of the first times I've seen it deployed in an online setting. It's something you usually see in games like Disgaea, Final Fantasy, and Star Ocean.
In each case there is an "endgame" level tier, whereupon class features and special abilities have all been awarded and there is no more advancement in that regard. However, there still exists more potential for "hard stat building through sheer time spent playing" in the form of the typical statistical gains players found in gaining prior levels.
This is also one of the first times I've seen this concept given a separate name and actually being a separate part of the experience. I believe the current problem some are having with it stems from this striation.
TL;DR Guys calm down, RPG's have been doing this for years. They've just been sneakier about it.