Many people don't realize how much loot will be given per boss as far as we know. The way it looks right now 10 man raids will drop 2 pieces of loot per boss. Now since blizzard wants 25 mans to be more rewarding that means it will have to drop a higher percentage of loot per boss.
10 mans: 1/5 or 2 pieces
25 mans: 1/5 or 5 pieces
^ This would mean the drop ratio is the same and since having 6 pieces drop per boss does not seem that much of an increase in the ratio 24% (6/25) compared to 20% (5/25) it is more likely to be around 7 pieces of loot per boss.
What does this mean? It means that either A) A LOT of the same loot will drop or B) The loot table will be a lot larger than it is now.
IF the table is increased that would make it very hard to get a certain item from a boss in 10 mans.
IF the same loot drops a lot in 25 man raids Blizzard might make some of the bosses share the same loot like it was in Naxxrammas.
No matter what happens, I believe Blizzard will find a very good balance between the two to keep people running 25 mans.