When the difference between the weakest player and the best player in term of gear is that small. Of course you need to reset it so everyone starts back at 0. The difference with Vanilla > BC > Wrath is that alot more people get the best gear possible. Im not talking about heroic mode DS gear. Im talking here about even the regular DS gear. If the difference was a couple of tier between the best and the worst, it wouldn't be that big of a problem. When only 1% had Naxxramas 40 on farm, the designer developped the game around the majority that wasn't that geared.
Hence why people killed Illidan while wearing T3 (or Kael, dont remember...). It was good like that. Because the majority felt dragged toward being better and having beter gear. It was also rewarding for the best to play as they could force themselves throught content easily. Now. they have to do a full reset or else they can't tell people with bad gear to live with it, as they are the majority.