I'm probably being dim for not noticing this earlier but I see the game mechanics being used to avoid content and I have to wonder if it's an exploit.
I realised it when I saw a character in a fairly nasty place (for me ) and the mobs cringing from them and thought - as you do - "What level is he?" Well the answer was level 12. And exp mobs for 19 were cringing?
The answer is of course obvious. Group with someone to whom they are grey and they go grey to you too. It is not dependent on range, they just have to be in the zone.
There are lots of quests that consist of visiting a dangerous place or cataloging a dangerous creature and do not require exp killing at all. This of course trivialises such quests.
Is this clever? An exploit? A bug?
I'm interested to see what people think.