Personally my comm goes to someone who performs above and beyond their role, dps or not.
Comms go to dps for things like use of goad, proper use of diversion/lucid dreaming, use of feint/addle, a mana shift/palisade/apocatastasis, warden's paean/nature's minne, shadewalker, cures/raises.
Healers get it for bringing high dps and no deaths.
Tanks get it for proper CD use and stance dancing appropriately to increase dps.
High dps as a dps is nice, but that's your job, I'm not gonna praise you for doing your job, I'm gonna praise you for helping make everyone else's job easier while doing your job.
And I know these are the things that get me a lot of comms when I run dungeons because it's the things that other people can see and appreciate.