Uh, they didn't. They finished #1 in week 1 of this season, though.
Not that it's hard if you play like 200 games more than anyone else and can completely rape the top comp (rogue/priest).
It's a situational comp that's heavily dependent on what comps you go up against.
If you get warrior/druid, ret/druid, say good night; you're pretty much ****** unless they're awful.