they only change the scatter
They also gave it slightly less health and more firepower, among other things:
From the changelog thread, post #7
Updates for June 13th, 2013
IS-2:
- Armor from 400 front/200 rear to 375 front/225 rear
- Pop from 14 to 16
- Health from 1280 to 960
- Price from 560mp/210fuel to 680mp/300fuel
- Reload time from 8.25s to 9s
- Scatter from 10m to 7.5m
- Acceleration increased from 1.5 to 2
- Rotation rate increased from 25 to 30
- 1 in 6 chance of 5 second crew shocked critical on target deflections
- Penetration increased from 110 to 140
- 25% of the shell’s damage is applied on non-penetrating rounds against enemy armor.
Worth noting too is that the tiger rear armor went up, as Endeav said. I think the buffs more than make up for the increased rear armor though, especially since they decreased the tiger's front armor. Despite that, the IS-2 is still a crappy tank for the gigantic amount of resources you invest into it.