I mean, is there an actual functional difference between
- The devs explicitly do the math to add healer DPS into rDPS to make sure that average total DPS can clear an encounter
- The devs use DPS and tank damage to set an encounter's HP, do some percentage screwery and hope healers doing damage plus some health reductions for suboptimal damage will make up for it

In one case they explicitly factor it in, in the other they know it's happening and...factor it in but less officially.