Lol 3 years ago it was WoTLK that killed arena, now it's cata, tomorrow it'll be pandaria or whatever this thing is called. Games progress, nothing is killed, they just evolve. It's so boring watching people repeat the same exact cycle of disdain, x killed y, y killed z.
that's easy to explain
it's because every expansion has been worse than the previous
wotlk was fucking shit and everyone was whining about it, but when cata came it people went "wow, wotlk wasn't that bad"