I think you are missing the point of his statement. It's not about separating one group from another because of skill. He says the game is about choosing the content you want to play. If they were to add a piece of gear with special stats somewhere in the game that would tweak or improve a player's stats then people will start to feel like they have to do that content to acquire that piece of gear. What this does is separate the people that actually do that particular content from the people that don't normally do it. This creates animosity towards the game and it's developers, because now you have the group that doesn't normally do that content feeling like they are being forced to do something they don't want to do to improve their character.

It has nothing to do with the personal skill levels of individual players.