http://www.wowmasteryguide.com/wow-classes/world-of-warcraft-warlock.php
Strength is of no use, if the World of Warcraft Warlock has to rely on melee, then he's doomed. The Wow Warlock's primary source of damage is DoT spells, so it just doesn't make sense to put a high investment into INT. Spirit may seem useful because it increases your manna regen rate. However, since a World Of Warcraft warlock has the ability to convert Health into Manna, it really makes sense to increase Stamina.