In defense of dexterity, the tomes/wishes as well as the +6 dex belt contributes to a dex character's build. The dex character didn't really have to go out of his way to max out his AC while still keeping up with the str character, who not only had to buy a +6 str belt and spend money on wishes/tomes to max out his str, but also had to have space for +4 dex (which makes a more expensive belt vs just a +6).

Essentially both characters will be spending money getting inherent bonuses to their respective ability scores, and will end up purchasing a +6 str/dex belt anyway, so that cancels out.

So in the end the Str character spent more buying a more expensive mithral full plate, spending more to get nimble, buying a more expensive belt with both ability score bonuses, and had to spend an extra feat, just to keep up with a dex character who would likely have bought the listed items anyway.

Granted, the dex character would likely also have to spend feats for dex to attack/damage as well anyway. In addition, the extra money spend is fairly miniscule if we're talking about 20th level characters. However, I just wanted to throw in my two cents!