honestly, i blame a combination of paladins and blizzards desire to "even the playing field" between all classes.
first, the paladins...they made life in late BC easy mode. the old joke of the pallytank who marks the boss with a skull as soon as he enters the instance and says "ok, go" isnt too far off the mark. people begged for pally tanks later on in BC because they could waltz into an instance regardless of class composition (just needed a healer) and tank everything effortlessly. for dps classes that lacked CC, such as dps warriors, druids, other paladins, and sucky warlocks, this was a godsend! no longer did you need to choose your instance group dps based on the CC they added. no longer did a clueless dps who couldnt CC bring a group down. you grabbed mr. pallytank, a good healer, two other dps of any class and off you go.
so, naturally, when wrath came out, blizz abandoned their idea of "niche" tanking (pallys as aoe, wars as single target, druids as a mix with pure hp/armor) in order to "normalize" raid encounters. they did this with raid buffs too. the problem is, it required each tank being elevated to the level of the pally tank when it came to aoe...or at least being passable when specced correctly and played right. thats great from a raid perspective, but for 5-mans the fallout meant you had four tank classes all capable of holding aoe threat off of healers without an issue, and, when given a few seconds (something even stupid trigger happy dps somehow manage to be able to do) are capable of keeping aggro from a whole group in time for it to be aoe'd down.
this also, again, has the side effect of increasing the relative value of "non-cc" dps classes. bringing a shadow priest over a mage is no longer a liability because the priest has no reliable CC. and so on and so forth.
incidentally, this also means when you *do* find a dps class that knows how to CC...man life gets much better. we have a mage in our guild who's a former grand marshal, great at pvp, and i know, on a gut, instinctual level, that if we are in pvp and i see a healer off in the corner with glowy hands, that said healer is going to be a sheep in approximately 1.25s (said mage stacks haste). said healer will then stay a sheep for as long as DR allows, followed by a deep freeze and a counterspell to another sheep cycle. its a thing of beauty.