Mistwell said:
Turning doesn't cause idiocy in your target, just fear.
And fear never, ever, ever causes you to do dumb things, or inadvisable things, or less than optimal things?
Furthermore, are you certain that every zombie and skeleton has the tactical finesse to understand the concept of withdrawing? The way I read it, turned creatures, particularly mindless ones, aren't interested in anything but getting the heck away from the divine caster. And they are so interested in that, in fact, that it distracts them from defending themselves adequately.
If they cannot flee, they cower (giving any attack rolls against them a +2 bonus).
Now, I will agree that nothing says EXPLICITLY that they double move when they "flee" rather than withdrawing. This is therefore a DM judgment. I simply happen to think it makes more sense for them to "flee" via double moving instead of withdrawing, particularly in the case of unintelligent undead who, it can be argued, cannot even grasp the difference.
Nevertheless, let's examine another assertion, namely that a double move is exactly the same as withdrawing. Here's a quote from Withdraw:
(Invisible enemies still get attacks of opportunity against you, and you can’t withdraw from combat if you’re blinded.)
I'm pretty sure that you can double move while blinded.