For my most recent random BG I got Strand of the Ancients. It's not my favorite, but I enjoyed it more than expected. Except for one thing: The DK who kept whining about heals. Then I want to play Team Fortress 2 and kept hearing people thank the medics no matter how often they died.
Does TF2 have a better community? Are DKs just antisocial fucktards? Maybe.
Or maybe it's that no one ever said anything at all to the medics. I didn't see a single typed word or anything on the voice channel (tough maybe I just wasn't in it). Nor was I hallucinating.
Instead it was the automatic response of the characters. When they get healed up, they thank the medic: "hey thanks, doc", "you're a great doctor!"
Is this an incentive for healers to heal? Certainly it helps that medics are terrible at offensive action, but no one has to pick a medic. Could the simple responses of the characters actually be a reward for those who play medics? They know it's automatic (at least I think they mostly do; I know I didn't for a while), so it's not as if they are thinking "this person was appreciative enough to say something." But people can respond to that which appears human.
Should BGs have a random "X loves your healing!" emote? Would that encourage more healing, and help to reduce the impact of that DK who wouldn't shut the fuck up?
I am leaving out a significant factor: medics heal by continuously firing their healing gun onto a target and get kill assist credit on the players they heal, meaning that they can easily rack up huge assist counts while staying just behind the front lines.