I don't know if anyone has mentioned this but back in 3rd edition, healing in combat was not as easy as some make it out to be because of the action economy. You only have so many actions that you can take a round and everyone is not going to huddle in a tight group so you can heal them with in reach.
My group never had a problem in 3E healing those in the group that have been hurt. At level 3, clerics had access to Close Wounds, which was an immediate interrupt (as if the damage never happened), which also had a range of 25 ft + 5ft/2 levels. At level 9, they had access to Mass Cure Light Wounds, also a ranged spell. And, by the time they get to level 9, they're most likely Hasted and/or moving faster than normal with a magic item, so can usually reach an injured/fallen companion on the battlefield.
We had in combat healing back in 1E/2E days as well - however, since clerics were more limited in 1E, it was less common. And, while clerics were better in 2E, they were still not capable of healing as much as their 3E/4E counterparts.
I think in combat healing should be limited, or should heal less.
Maybe in combat healing is less effective? A Healing Surge (or whatever you want to call it) heals 10% of hit points in combat, but 20% outside of combat? You can say that the clamor of battle makes healing less effective than when the cleric has the 10 minutes to properly invoke his or her deity in a proper manner.