I'm also surprise that wrath is above TBC, i guess, if this poll was made 1-2 years ago, TBC would still be king (as a matter of fact, i have seen quite a few of this kind of poll, pre-mop, TBC always end up ahead)
For this reason, i agree that, there must be a good part of old school gamer (not all of them obviously, since vanilla - tbc still got vote) that just moved on, that is not only don't play the game anymore but don't come to these forums.
It's not big secret that they have been huge turnover of player in wow, in fact, from the people i was raiding with back in TBC, maybe only a few remains, the vast majority have quit (me included). i still keep teamspeak contact with old friend, bot not ingame, $15 just to chat is pushing it.
So yes, since the population of wow has barely changed since TBC (11 millions at the end of TBC, 10 millions at the begining of MOP), i suppose that there are as much new player that came into the game, most possibly durring the wrath period, which explain the poll.
The problem with wrath, is that it alternate the best and the worse. Naxx 80 was awful, boring and far far too easy. Ulduar was maybe the greatest raid of all wow. ToC possibly the worst raid tier of all Wow. ICC was ok, but i did not like the constant nerfing. Or more exactly, i feel that people that clear it pre nerf should have something special. title or tabard, or mount, anything.
I agree that the first 6 month of cataclysm were great. Nice leveling, though the zone were too far apart, the dungeaon heroics were fun and challenging, people needed to manage mana and use crowd control spell, really fun. being able to cheat the dungeon finder with item in bags were a big mistake from blizz, which contribute to the general feeling that dungeons were too hard, which there were not.
Raid were interesting, nice trash pack in BoT, nicest trash pack we have had in a very long time. Interesting mechnics for the boss.
But the quality degrade after that. No raid in 4.1, just two rehash 5 man content. 7 boss raid in 4.2 and 8 boss in 4.3. It's not so much the number of boss, but the design of the boss, especially in 4.3 Far too repetitive, often enough, DS boss had 2 phase that just repeat until enrage. Deathwing could be one of the most repetitive and boring fight of the game, as bad as raid boss from molten core.
Can't comment on MoP, never played it.