Several people have posted that affliction is higher dps. While this is true, it is also significantly more complicated. If he isn't executing destruction effectivly, then it is unlikely that switching to affliction will help matters. If anything, you might push him to spec 0/41/30, which is the simplest playstyle that can still put out reasonable dps.
It sounds/looks like he was destruction in BC and has since thrown together a spec that looked good to him and continued to play the same way without bothering to do any research as to how to play effectively in wotlk. Even a cursory search into wrath theorycrafting should have shown him that he has things all backwards. Anyway, the first post in the following three threads should give you enough info to do the work he has decided not to do:
Affliction:
http://elitistjerks.com/f80/t37900-d...arlock_thread/
Destruction:
http://elitistjerks.com/f80/t38033-m...ction_warlock/
Demonology:
http://elitistjerks.com/f80/t37474-demonology_thread/
I would also push him to get rid of the spell penetration enchant and gems. There is currently no reason to have spell penetration for PvE content and anyone who tells you otherwise is mistaken. He has no enchants on his helm or shoulders. Even if he just went back and got the enchants from TBC, it would be an improvement. As far as hit goes, he could easily reach the hit cap just by changing his gems to 16 hit.
Good luck.