Let's examine a little remembered tactic from WAY back in the days of roleplay.
Many characters were designed around the concept of having a good AC and making attacks against them fall to the wayside...
But some characters developed the idea of DGH as even better than AC.
What is DGH? It's called 'Don't Get Hit.'
See, if you have really good DGH, your AC became superfluous and unnecessary. Mages exploited this by using the spell Stoneskin to negate what few hits came their way. DGH would win the game for them, when AC was a non-issue.
Warlocks have one of the few abilities to give themselves DGH in 4th edition, altho it gets renamed to 'Don't Get Targetted.'
DGT Warlocks favor Dexterity, not for the bonus to AC, but because of the bonus to Stealth. So long as you keep moving, you can remain Stealthed, enjoying the fact that a) Most enemies won't even realize you are there. n) won't target you if your existance is unknown, and c) Even if they -do- know you're there, you still have that +2 to your defenses from concealment.
Not to mention, the benefit this tactic gives to your -to hit-, because of the +2 you'll get from combat advantage -all the time.-
So compare... is the +1 to hit +1 damage from that extra point in Charisma comparable to the +2 to hit +3 damage from combat advantage and Astral Fire?
Yeah.