@Graylo:

If so many former 25-man raiders really preferred 25-man raids, why are all the 25-man raiding guilds having so many issues with recruitment? The fact is that the people raiding 10s for the most part don't prefer the 25s.

I think mostly what has died off is the casual 25-man guilds. In Wrath, most 25-man raiding guilds had a core group of 10-12 raiders, and the rest of the 25 that were mostly carried along. The core raiders used the 25-man to get the better gear, and ran their 10-mans for actual progression or hard modes. Once lockouts were shared, that model was gone and they were done carrying the rest of the group since the better loot didn't exist anymore either.

On my server, the most of the progression-oriented 25-man guilds are still there raiding 25s (and they're almost always recruiting). However, there were several much more casual 25-mans that are now gone. In addition, there used to be 25-man pugs I'd occasionally hop into since I was in a 10-man raiding guild, but I haven't seen any of those since Cata released.

It seems 25-man raiding is still popular in the world-first progression scene. However, I think the reason 10-man raiding has become more popular at more casual levels is that it is much easier to find a smaller group that fits well together in terms of skill, raiding commitment, and personality.