Blizzard hotfixed in a significant change to Diablo 3 multiplayer over the weekend. Previously monster health and damage would stack depending on the number of players in the game, now Blizzard have completely removed that damage buff. Monsters will still have more health, but they won't be any stronger. That applies to co-op games across all difficulty tiers, and is excellent news for groups getting wiped in seconds by top tier hero mobs on Hell and Inferno.
2DayBlog.com
See also:
techblog, Diablo 3 hotfix removes monster damage boost in co-op, Inferno teams breathe sigh of relief
