Up until 4.2 hits, shadowpriests currently deliver about 80% DOT damage and 20% direct damage during most combat fights. This is way higher bias towards dots than has previously been in game and meant that compared to less dot-baised classes, hit had a greatly reduced stat value as a missed dot could simply be recast with only 1 GCD loss of dps. When the 4.2 patch goes live the balance will revert to a much more (historically) normal balance.
Quote from: Patch 4.2- Shadow Orb Power now increases damage by 1.45% for each point, down from 1.5%
- Devouring Plague damage has been reduced by 12%, from 1240 base damage to 1088.
- Mind Blast damage has been increased by 12%, from [ 1277 - 1349 ] to [ 1431 - 1512 ]
- Mind Flay damage has been increased by 12%. From 501 to 561 shadow damage.
- Shadow Word: Death damage has been increased by 12%. From 301 to 337 shadow damage.
- Shadow Word: Pain damage has been reduced by 12%. From 1326 to 1164 shadow damage.
- Vampiric Touch damage has been reduced by 12%, from 540 to 475 Shadow damage.
TL:DR 4.2 nerfs dot damage and buffs direct damage. DD means higher emphasis on being hit-capped.
So this means being hit capped in 4.2 will become essential (imo) again, so start planning your gear/gems/reforging appropriately.
(the shadow orb change is not a nerf at all, just a tooltip correction which was rounding the in-game 1.45% to 1.5% in the tooltip)