One of the upcoming changes in the new patch is that Damage-Over-Time spells will now have their damage reduced by resilience. Some DoT classes see this as unfair, because resilience is a stat targeting critical hits, and DoTs cannot crit.
I think the reason DoTs need to be reined in a bit is that their normal counters are much less effective these days. Traditionally, the downside to DoTs is that they can be Cleansed or Dispelled. But Cleanse is no longer as powerful as it once was, due to three new factors in TBC.
First, Unstable Affliction punishes you for Cleansing. It does a significant amount of damage, and the Silence effect is a killer. It is a superb guard for the other DoTs.
Second, there are several new talents which increase the chance of resisting the Cleanse.
Finally, many classes are able to apply 2 magic debuffs per global cooldown(GCD). While Cleanse only removes 1 magic debuff per GCD. Shadow priests in particular are insanely annoying for this, as all their spells add an extra Shadow Weaving debuff. This means the Cleanser is always falling behind. Affliction Warlocks use Shadow Embrace to accomplish the same thing.
As well, Cleanse is an entirely defensive action, and that means that the attacker has tempo, or is controlling the fight while the defender is Cleansing. While you Cleanse you can't use special attacks or heal. In general, because of tempo, defense needs to be more powerful than offense to be a viable tactic.
These three factors have conspired to significantly reduce the power of Cleanse. Thus DoTs need to be reigned in using another method, which is Resilience in this case.