I don't want to get too pedantic, but as someone who's been playing clerics in D&D since the early 1980's I have to disagree with the statement "Turning is insta-killing" in AD&D. While not an official source, the SRD
here pretty clearly states the reality of Turn Undead in 3.5:
Effect and Duration of Turning
Turned undead flee from you by the best and fastest means available to them. They flee for 10 rounds (1 minute). If they cannot flee, they cower (giving any attack rolls against them a +2 bonus). If you approach within 10 feet of them, however, they overcome being turned and act normally. (You can stand within 10 feet without breaking the turning effect—you just can’t approach them.) You can attack them with ranged attacks (from at least 10 feet away), and others can attack them in any fashion, without breaking the turning effect.
Destroying Undead
If you have twice as many levels (or more) as the undead have Hit Dice, you destroy any that you would normally turn.
So, by definition, if an undead is destroyed it is NOT Turned. Turning is when the undead cower, flee, or are commanded. Flee/cower/command is the core of Turn Undead in almost every edition, with the min/max bonus of destruction for those exceptionally powerful compared to the enemies they face. It's not meant to be the "default" in any pen and paper session I've been a part of.
While there is plenty of room to argue about the stun effect, it does tend to mimic the intention of Turn Undead, in effect if not duration. Historically, DDO players have not considered Turned undead to be a successful tactic, opting instead for a simplification to "destroyed=worked". This is fine, but destroying undead will remain a part of Turn Undead. It's just that the intention of these changes is to have Turning get far more usage and effectiveness across the level spectrum rather than a binary "worked/didn't", which can be a challenge to maintain across the spectrum of level 1-30 and beyond (in terms of dungeon CR).