There were several encounter mechanics where the numbers scaling for 10-man meant that the difficulty was higher than in 25-man. Watcher particularly notes the interaction between Malice clumps and Iron Star triggering. In 25-man, the Malice groups, a total of six players, were never large enough to trigger the Iron Star, when they inevitably overlapped with Bombardment in the fourth Malice. On 10-player heroic, the Malice clump size of three in total would also trigger an Iron Star in the fourth Malice. Now, in 10 Heroic, the Iron Star trigger clump size is four, bringing it in line with 25 Heroic.
Additionally, Garrosh's health is reduced by around 5%, and Minion of Y'Sharrj health is reduced by 10%. DPS checks for 10 Heroic were causing guilds to try to single-heal the fight, and 25 Heroic players are able to kite the adds while 10 Heroic guilds don't have the spare manpower. These changes show the process Watcher has discussed in the past, specific targeted nerfs, and will bring the two sizes in line. Hit the break for his full post.