Lore just posted this.
"We made this change because, even without the Tier 16 4-piece bonus, we felt that Balance multidotting was too strong. On top of that, with enough mobs available, the Balance rotation was devolving into just Moonfire/Sunfire and spamming Starsurge constantly, to the point of completely ignoring Wrath and Starfire.
The way this works under the hood is by multiplying the base proc chance by SQRT(x)/x, where x is the number of mobs that have Moonfire or Sunfire active. Note that the proc chances are calculated per spell – Moonfire doesn’t count against Sunfire’s proc chance, or vice versa. So as an example, if the base chance is 30%, and you have Sunfire active on 1 mob but Moonfire active on 3, your Sunfire will have a 30% chance to proc Starsurge on a crit, and your Moonfires will each have a 17% chance.
As an aside, this didn’t make the latest PTR push, but we’ll be buffing Wrath, Starfire, and Starfall by 10%."
Source
http://us.battle.net/wow/en/forum/to...5458?page=1#19