@Alsides

What game have you been playing? The 25's are the ones people are pugging. You have more slack if a person dies. You can afford a spare tank or two. You can afford to bring an extra healer. Group synergy isn't as important. We had been doing 10 mans for a couple months as we didn't have enough for 25 raiding. We are a really tight knit group so its hard to recruit. So instead we have been clearing 3 wings of naxx25 with 16 to 19 people for the last 3 weeks. The only 25 that MAY be harder than the 10 version is EoE and then just barely. Just last night I pugged a 25 sarth+1.

As far as studying. In a 10 man everyone needs to know what to do. In a 25 as long as the 5 people that are doing something different know what to do the others can stand around slackjaw mashing 11111211111211111234. If your mage dies at Gluth in 10 you are boned in 25 one of your other 5 mages picks them up.

As for Ulduar it remains to be seen if 10 is easier than 25. If it is a drastic step in the other direction then I agree 25 should give better rewards but as for NOW 10 is harder. So it should give equal or better loot.