They were overpowered they said. In fact the Boon of Protection was "10 times over its budget" in benefits to the Monk, and was "quite simply a mistake" to let slip.
It's early days and other classes will be getting closely scrutinized now that Diablo III is among the masses. There have been tweaks to the Wizard and Demon Hunter too.
"In general class balance is an on-going investigation, and by no means do we believe the game is now perfect, but we're also seeing evidence that supports (with a few nerfs to wizard and demon hunter) the monk and barbarian are not as bad off as they seem," posted Blizzard community manager Bashiok.
"A large part of the monk and barbarian designs are based on survival models that mimic the concept of the class itself. The idea of a monk is that he survives through being agile and difficult to hit, and his healing and survival scales particularly well by focusing on mitigation stats like dodge, resists, and armour."
"The concept of the barb is that he survives through a huge health pool, and healing himself through damage (%life on hit stats), which is potentially a bit obvious with all the life return skills but can't be overstated."
"The game is young, there were some skills that threw things out of whack, and we expect the landscape to settle out a bit more evenly. Or at least change again so we can continue to monitor the impact."
"Maybe we're wrong, maybe there's no current chance for monk or barbarian to compete with ranged, but our current suspicion is that's incorrect and until we know for sure we're not going to turn any dials."
A changelog is expected to be released today so we can know what's been tinkered. So far the Monk's nerf hotfix has been spilled on by Bashiok: "The Boon of Protection rune was approximately 10 times over its budget on the benefits it provided, and it was quite simply a mistake on our part to let the rune ship as it was."
"We don't intend to take these quick and drastic measures often, but considering the severity of the issue, we felt it important to correct it swiftly." The change made: "Amount of damage absorbed is now capped at the amount of healing provided by Mantra of Healing in the first 3 seconds after activation."