Another reason that Dex is better for frontlining when you're a Cleric (or any caster, really) is that not getting hit is particularly important when you're likely holding a concentration spell. Sure, the concentration check may save you... But why rely on that when a your AC means a lesser chance of having to risk it at all?
This is just saying that Dex is nice because it gives you extra AC depending on your armor allowance. Nice doesn't necessarily equal better.
