In Mists of Pandaria, rather than retroactively nerfing legacy content, dungeon bosses will drop the same amount of gold per player, regardless of how many players defeat them. So if a boss drops 100g for 25 players, it will drop 20g for 5 players. This change is retroactive for all dungeons from previous content.
The full text of Watcher's clarifications as follows.
It's open warfare between Alliance and Horde in Mists of Pandaria, World of Warcraft's next expansion. Jump into five new levels with new talents and class mechanics, try the new monk class, and create a pandaren character to ally with either Horde or Alliance. Look for expansion basics in our Mists FAQ, or dig into our spring press event coverage for more details!