http://www.youtube.com/watch?v=8rd0-...layer_embedded
A little more explanation, for the inevitable haters: (Wall of Text)
I played WoW in vanilla, and started raiding in BC at a very casual level. I experienced the sense of wonder and adventure that he describes all the same, even though I never got past SSC, but he does a pretty good job explaining that aspect of his argument. Instead, I'm going to explain how it's logistically a much better approach to raiding as well.
With 2 or 3 tiers total, (2 released at the start of the expansion), Blizzard makes the game better for everyone involved. The key here is "old" or "outdated" content. Essentially, when Blizzard "boosts" players to the current tier, so they can see the content, the involved players completely skip over other entire raids, essentially wasting the content. Instead of having two different raid tiers, Blizzard wastes their old raids and instead makes people repeat the same raid again to progress. Here's how a change to multi-tier raiding effects each skill group. This assumes two tiers ar the start of an expansion, referred to as T1 and T2.
PUG raider:
Doesn't effect them too much. When the xpac first releases, PUGs would be rare, but eventually PUGs start coming up for the T1 content. This is basically how it already works with the current system. Since the T1 content would be comparable to normal mode of current raids (perhaps a little harder), PUGs would spring up at around the same time. There would not be a significant difference in amount of content seen for a PUG raider. Basically, PUGs just work through the T1 content instead of the hardest content, but they don't actually see less of Blizzard's work. But of course, for the reasons the video explains, these people will be MUCH more driven to experience more content, rather than if they have already killed the last boss. It's really okay for a raider only doing PUGs to not see the hardest tier. In fact, coming from an extremely casual raider, it really makes the game seem like such a greater entity, and keeps you playing, knowing that there is always more difficult things to experince.
Casual Raider:
Casual raiders benefit the most from multi-tier raiding. Essentially, they will progress through T1, just like they normally would. But there's that drive to get to the harder, more prestigious content, and the sense of adventure when you get there, just like the video describes. But furthermore, when you finish the first, T1 content, you can progress to entirely new content in the form of the shiny new T2 raid.
Hardcore raider
Hardcore raiders will see all of the content Blizzard produces anyway, so there isn't much change here. In theory, T2 should pose a real progression challenge to hardcore raiders, which it doesn't really do anymore. I understand that raiders are better than they used to be, but I still think it should be possible. Additionally, there's the reward of more prestige in all of your shiny T2 gear, which all of the other raiders admire and aspire to.
On attunements:
I don't think attunements should be needed. The content difficulty barrier should be great enough that it makes sense for the group as a whole to finish each T1 raid before progressing to T2. And attunements can be annoying for players trying to jump into a raid squad on difficult content.
When Blizzard adds a new tier
First off, I think it's completely fine to add a new tier before the last one is complete. It completely removes farming time for hardcore guilds in T2, and creates incentive to beat content. However, I believe that when T3 is added, there need to be a few nerfs for T2 and T1, but NOT too many. Natural acquisition of gear over time makes this content easier for the target demographic anyway, so these nerfs do not have to be big. The nerfs are so the jump from T1 to T2, initially designed for hardcore raiders, is more accessable for a casual raider, and so the T1 raid becomes slightly more puggable. Again, the idea isn't to remove the Heroic dungeon step, but to make a jump from heroics to T1, intended for casual raiders initially, to be accessable to PUGs. T1 becomes the puggable tier, T2 the casual raiding tier, and T3 the hardcore tier.
PUGs and casual raiders will have something to work towards. And of course, when patch x.0 comes out, they should be able to progress through the T3 content that they didn't quite finish to finally experience ALL of Blizzard's content, not just the newest.
I really can't see how this system is worse than what is currently in place. It uses all of the content instead of just part of it, eliminates repeating content, gives every kind of player something to progress on, and allows most players to eventually see ALL content (not just the new stuff), if they put forth the effort. And for those who never fight the final boss, it's really okay. Just the fact that it's THERE, and its POSSIBLE, makes each kill all the more sweeter.
Thus, the sense of adventure and wonder is recreated, and the World is sound again.