Churches, Gods, and Domains.
If Churches/Gods were added to the game, clerics would need to decide which church/God they belonged to, if they desired to belong to one at all. In ALL churches, healing supplies could be purchased. If a cleric goes to their church they get the items at a much reduced price. The God they worshiped would grant them a few minor spells to supplement there beliefs. In PnP these are called Domain spells. The "type" of cleric you are gives you benefits in the area of expertise. For example the God of the elements (dont know if that is an actual DnD God, just making up) could give your comet fall a +2 to DC. The Healing God, could give your heals improved HP. Etc. Etc. Etc. This is very similar to the focuses spell abilty, but given based on belief or worshiped God.
These churches could also provide benefits for other God fearing classes, such as paladins. The paladin may need to give a monthly stipend to support the church in return for some holy potion or enhancment.
There are a variety of tanks in the game, a variety of casters, why not a variety of clerics. (without splashig in another class)