Though rogues get very high dmg,most end-game guild only take 2-3 with'em mainly because alot of bosses do an aoe to everyone in melee range,and every healer that has to heal them,is one less that can focus on tank(s).Locks lack the panic buttons(only soul shatter for aggro)Basicly mages are mostly represented as dps,good overall dmg,ranged thus most times less healing + they have panic buttons like ice block,invisibility,blink(for any aoe or bad positioning after fear etc) and maybe ice barrier for the very few endgame frostmages +I have yet to see a raid without mages,they're just damn nifty for food/drinks.