No one has access to use the Search function, don't feel bad.
Onto the real question.
Yes it may strike you as odd to Think about what DEX really controls, manual dexterity, ability to dodge weapons, etc. But when it comes down to it I find it balances out really well. Trying to come up with another stat, such as Agility, really messes with the calculations. I'm not saying the system is perfect in any sense of the word. I am saying any who have tried to split any of the core 6 ability scores into two different abilities seem to get something missing in the mix. Something seems to be missing in the long run.
It is no different as to why anything else isn't included, or is rolled into something else. I'm sure we could come up with houserules to put honour into CON but it wouldn't really make sense. Similarly, trying to figure out what aspects of DEX go into Agility or remain in DEX are going to mess with your brain.
Fundamentally I think it should remain one ability, just like any other should remain one ability. I would not like to suddenly have to come up with 12 stats at level one because they got split. No Body and Internal Chemistry (CON) scores, Will and Perception (WIS), Force of personality and Looks (CHA), etc.
ps. To nonsi256: No offense, I have read much of your Final Codex of rules and I find them lacking in many of the same ways as the base system. Where the base system excels is not having to re-learn a whole bunch of new stuff, having to convert anything already made for the 3e d20 system and not having to adhere to your interpretation of what the game should look like. While I'm sure your rules work for you and I'm happy about that, I really don't think they will work for everyone, nor do I suggest that you offer them as a remedy to questions like the one the OP asked.