I think, like you said, they could have just released a single 40 man with gear on par with the top 25 man instance which would have transitioned the game perhaps a little smoother, in theory. But really I think in practice it would be exactly the same thing and they probably just figured they'd save themselves the effort. There's like maybe 10 guilds in all of WoW who would do that instance because they have 5 solid tanks and don't want for any to sit out. So they can field the people. Absolutely every other guild would just take their 25 best and hit the 25 man. And that 40 man instance would be criticized for being a waste of developmental energy and resources, as it would sit largely unused (and eventually, totally unused, even by the original 10 once they slim down). So why would bliz bother with a token gesture for a handful of guilds that are going to be fine anyway? I think once blizz decided they were going to shift focus from 40 to 25, they just had to run with it, it turns out the best that way-- anything else and they're doing two things half as well as they could be doing one thing (i.e. people on both sides are only getting half of what they want, whereas if they just made the transition they could be enjoying the game the way its meant to be and to its fullest).

I guess you could say they should make that token 40 man have the best loot, in which case nothing changes and you're left with what amounts to one true end game instance. In any case, is it going to be painful? I think a lot of that is people just looking for a reason to support the status quo. I mean, argue against it or for it on its merits, I don't think the cost of transition should really be one. Takes eggs to make an omellete and all that (and really this was their rationale for not doing it sooner, they figured the expansion is going to be like a new game and people can choose to buy it or not, whereas with live it'd be pretty bait and switch. If you think of TBC as WoW2 it makes a little more sense, at what better time could they make a much needed change?). For an elite few who run honor farming perma groups the upcoming changes to pvp will cause growing pains, but its an altogether better system so why fight it? I wouldn't want to wallow in shit forever just because getting out might hurt in some way. In any case, those people who have the meta-game advantage of running those honor-monopolizing groups are in the minority and this is an egalitarian change that should rightly offend them.

Then again, if you don't acknowledge that 25 mans are going to be straight-better then this all seems pointless. But who thinks that? Probably a similar proportion of the playerbase that run honor farming groups.

The other thing being, of course, that 40 man raids allow for more complexity. But there is of course a relationship there, the "better" an encounter is, for its complexity (people required), the fewer people actually get to see it. And I think particularly here people suffer from top-guild-myopia. There's always one guild on each server that anyone with skill and ambition aspires to be in. For every one of those guilds that fields 55 great players, there's 10 others just trying to cobble together 40 non idiots. One might say, "that's too bad", but this isn't the galapogos islands where chance and fitness determine the natural order, this is a game made to make money by entertaining people-- that means, "no, too bad for you asshole."

So anyway they're trying to strike a sweet spot, and since the system as-is, despite however comfortable some people are with it now, is flawed in their eyes, they're going to change it, with little regard for those who currently like its flawed implementation.

Two comments:

1) on the hybrid-role side of things, I find it interesting that Delemos suggests that 25-man raids may in fact encourage hybrids to some extent. I say this because DnT has always given the impression - at least to people externally - that as a guild they emphasize min/maxing and optimal specs across the board for their raiders. It will be even more interesting to see if TBC actually works out that way.

2) on the idea of phasing this in with at least one 40-man raid in the expansion. Personally, I think Blizzard is making the right decision to make a clean cut at the time the expansion comes out. Why? Simply this: I think the new content in the expansion will keep people around longer through the transition. And if you stick around longer, your chance of joining or deciding to form a new raiding guild are higher than if you don't stick around at all (duh!)

Imagine for now that TBC was a year away and Blizzard announced that their next instance was only 25-man. And you were one of the people who was not in the top-25 of your guild. What would you do? Me, I'd probably cancel my subscription. I might look for another guild or do a server transfer but there would be a high probability I'd decide now was the time for a permanent break from the game. Because there really isn't anything in the non-raiding game right now that is available that would keep me going for long. I believe that is what would happen if TBC came out and they gave us one 40-man instance to play in. It would keep people around, and part of their guild, just long enough to exhaust all the TBC content. When you mastered that instance, it would cut those extra people free at a time when there was nothing left to keep them in the game.

But TBC is right around the corner. I'd play it for a while even if I didn't belong to a raiding guild anymore just because I enjoyed the 1-60 levelling process so much and I enjoyed 5-man instancing with friends. If I hit 70 and hadn't found a new home, I'd probably leave then. But give me another 3-6 months of non-raiding fun in the expansion and I may well find a new group to play with and form a new guild to keep me going at the end of it all.

its unlikely to happen but all these people who say 'finally we get rid of those 15 scrubs in our guild' better hope blizzard doesnt tune their encounters to this attitude
if they say 'ok, guilds will have 25 non-scrubs now, lets make it a bit more difficult', you might find yourself on the short end of the 'omg do your job!' comments all to quickly

We looked at this from an external PoV, and tried to give an unbiased opinion on the possible positives and negatives of it. We do, "encourage", min-maxing, and encourage might not even be a strong enough word. If you don't perform, you don't get a raid slot, and the odds of you being able to perform up to the level of other members of your class with a non-optimum spec is virtually non-existant. For example, one day after innervate became a core talent I asked during a raid if we had any druids without swiftmend, and the answer was no. No one told them they couldn't spec something else, and I suspect you could easily spec 24/0/27 (or whatever the correct numbers are) or 30 feral 21 resto, and still perform up to an equal level, but they all chose to spec swiftmend.