Eliah Hecht's article "25-man gear should not be better than 10-man gear" sparked a lot of great discussion with our readers and, I think, some illuminating poll results as well. The majority of responders believed that giving 10-man and 25-man raids the same loot table would result in a significant drop in popularity for 25-man raiding. Overall, I tend to agree with this, but I also think that Eliah touched on something that speaks to Blizzard's evolving sense of game design, much of which is evident in the transition between late Burning Crusade and Wrath.
I would like to call this the Sunwell effect, or "ingame rationality." To wit: don't incentivize players to behave in a manner contrary to your actual design interests. I believe this played a huge role in the differences between BC and Wrath raiding, and that it underlies why the 25-man loot table has to remain superior to its 10-man counterpart.