Any specifically AoE spells should be ground-targetable.

[Alhanelem]

I've never seen this feature employed in most.

You haven't played too many RPGs then, have you. The Dungeon Siege series, Every PC D&D game e.g. Neverwinter Nights series, Dragon Age series, D&D Online, LotR Online, practically every other semi-succesful MMO (except for the more fast-action based games like Dungeon Fighter or Vindictus), and going outside of RPG land, virtually every RTS game made since Warcraft III. Virtually every other kind of game these days where the precise placement of something is valuable, has had a targeting indicator. Even bleeping Tetris.

It's just simply a good interface function- not a game-defining feature that makes your game a WoW clone.

I think people jot back to WoW because somehow everytime someone makes a suggestion "oh its an MMORPG standard"

It's not just an MMORPG standard. It's a standard in almost any kind of game where you need to carefully position objects or target anything anywhere.

You don't guess where your AoE hits, if you see 4 mobs clumped up, you can guarantee it will hit them all.

No, you can't guarantee that. The game doesn't tell you or give any indication of the size of the area of effect. You have no way of knowing for sure until you've cast the same spell a million times. And what if you only want to hit 3 of those 4 mobs? With ground-targeted AoE, you can do that. Otherwise all you can do is hope only one of them moves and moves far enough. Also bad is the fact that apparently some spells are radial AoE and others are conal, and the game doesn't even have the courtesy to let you know that before you cast.