Yes; but keep in mind that people continued to do TK:Eye even after BT released because of the stupid attunement. You had to kill KT and Rage Winterchill personally to get attuned to BT. Attunement sucks.
I really wonder how many guilds would have continued to run TK after BT release if there was no attunement for Mount Hyjal or Black Temple.
Well, look at the item levels though. Kael dropped 141 loot, the same that you got in BT. That's on par with having Heroic Empress and Sha drop the same ilvl loot that comes out of the Thunderking normal raid.
Also, if you look at much of the t5 loot tables, you'll see 134 ilvl gear, up to 138/141 on end bosses, and then going into t6 you see 141 level loot. At that point, you're looking at 1/2 to 3/4 of a spread of what we have been normal and heroic loot now, and they are looking to go with 502 ilvl lfr gear. The gear inflation right now in MoP is astronomical, facilitating the deprecation of old content.
Yes, but that had it's own problem. I.e. with new players and recruitment. For example in Vanilla WoW, to do well in AQ40, you needed to be geared in BWL/MC gear. So, if you rerolled a toon or a new level 60 in greens and blues, AQ40 was out of the question. Conversely, attrition, player burn outs happen. So guilds have to recruit continuously. A guild in AQ40 would find it impossible to recruit new 60s-- just didnt make sense to recruit someone in Dungeon gear when AQ40 expects you to be in MC/BWL gear. This sorta forced guilds working on AQ40 to clear MC/BWL every week with their new recruits -- thus adding to the burn out cycle.
In WoTLK and Cataclysm, they solved this problem by updating dungeon loot and new VP/JP gear so that new players/alts can come upto speed ASAP. We know that there are no new dungeons in 5.2. So, I assume that they expect us to run LFRs (5.1 ones) to gear alts and new players and get them ready for 5.2 raiding after 5.2 release.