Many moons ago, raids were 40 man affairs. You had to really have your shit together as a guild to pull off the organization required to run one of those. It did mean that many people never got to see 40 man content unless they dumped their friendly/laid-back guild in exchange for a hard core raiding guild that while may have some nice people in it, was more worried about raiding than maintaining online relationships. So, for this reason and many others, Blizz dropped the 40 man raid in favor of a 25/10 setup.
Some raids were 25, some 10. You were introduced to raids in 10 mans, then moved up to the harder 25 mans. Great. If your guild was just starting raiding, you had a place to get your feet wet while recruiting more people to progress into the harder content. Sometimes, two 10 man guilds would join to form a 25 man guild. Whatever worked.
Then Blizz started this whole all raids are both 10 and 25. Ok, fine. If you like 10 man, or your guild is just starting raids, you could do 10 man, but if your guild wanted to take the time to bring together 25 players you would get better gear. They also added heroic versions of each so people who really wanted a challenge (and better gear) had something to move up to regardless of the size of the raid. Of course, what's the real annoyance is that heroic mode is on a per boss basis. Blech!
This new changes offers no reason for anyone to do 25 man raids. Why would anyone want to take the time to gather up 25 people to do what they could with 10? So what if you get a few more drops per boss? You could just run two 10 man raids (or 3 if you add a 5 more players) and get even more drops per week per guild. This notion of a guild running 2, 3, or 4 10 man groups per week defeats the whole "10 man is harder to gear" argument. Sure, you have less drops per player per raid, but as a guild, you can progress faster since more players (and alts) have access to better gear.
This is especially true if you have the lockouts on the same timer. If you have to choose between spending an hour gathering up 25 people to raid or just go with the 10 that are there, you're going with the 10. And if it's a multi-night raid, waiting for the same 25 people to show up on time just doesn't always work. Now, some people would say that with multiple 10 mans, you need more tanks (or specific class tanks) and healers. But blizz has already started the blanding of tanks/heals. No longer is one type of tank or healer preferable over another for certain fights, so you can form 10s easier.
Another thing that Blizz announced is that they plan on the first tier of raids to be designed for people geared in some blues and crafted/heroic purples. That's all fine and dandy; however, with t9/10 gear being given out like candy and the cap going up only 5 levels, are blues even going to be an upgrade? Plenty of people with t5/6 in BC wore that same gear right into Naxx and that was a 10 level cap increase!
As far as multiple, shorter raids per tier, I'm all for that as long as it doesn't also end the long raids. I loved that in BC you could do Mags and Gruul in a short time and felt like you accomplished something, but if you wanted a full t4 set, you had to do Kara which was long. I like that you had to go to multiple raids to gear up, not just farm the one place week after week. I especially liked attunement, so you had to do the previous tier raids at least once before moving up (yeah, this is long gone to my dismay).
As I read other people's blogs and tweets regarding this topic, I see the for/against crowd made up of 10/25 raiders respectively. People who love doing 10 mans get the epic win. Do the same thing they have been doing because they don't like to spend all their time gathering up 25 people to raid now get all the benefit of a 25 man (gearwise). People who have spent the last year nurturing a steady group of 25 people to raid so they can get the top-notch gear are now being told that all that recruiting was a waste because they can just run 10 mans for the same drops.
Basically, this is the end of the 25 man raid.
And this really doesn't surprise me in the slightest. All of the changes that have been made in the past 8-12 months have had the effect of making a game that was about taking the time to experience an online world/community into a bland console game. It's becoming a game that is about "winning" or "beating" the game rather than experiencing it. It's about leveling the playing field so that everyone can "win". It's become a race to the end rather than enjoying the ride along the way.
These changes to raiding are just another step in the wrong direction.