to give you an example of sources outside of the healer classes that provide risk and reward.

DPS:

Blood for Blood: Take more damage, to deal more damage temporarily. Using this in savage content at the wrong time can kill you, but using it in the right time will make your damage go up without suffering the consequences.

Tanks:

Tank Stance VS DPS Stances: One allows you to hold aggro better and take less damage, the other enables you to deal more damage but you lose the mitigation.

If we were to take all risk away from healers, then I guess we should also give all tanks a passive 20% damage reduction with no effect on damage dealt, and give all DPS a 10% damage increase with no increased damage recieved... because you know, we wouldnt want people to think about their choices, we just want them to put their face on their keyboard, and just hit buttons.