When it comes down to mastery, Blizzard can be a little bit hit or miss. There are some classes or specs that love it, while there are plenty more that find it near worthless. When it comes to warlock specs, there isn't much of a difference. Well, so maybe there is a little bit of a difference; no warlock spec particularly loves or stacks mastery.
From an outsider's prospective, it would seem rather odd that mastery wouldn't be a better stat; after all, every warlock spec has nothing more than a flat boost to their damage for their mastery bonus. The problem, however, is in the dual nature of warlocks. With more focused or limited mastery, will warlocks be able to continually sustain themselves throughout the expansion? Further, will the scaling of affliction's mastery cause new issues once again?