As I mentioned in another thread, a lot of people forget that a lot of caster gear has both INT and MND on it, even though they do completely different things, because it's shared by 2 different jobs. It's not farfetched to have STR and DEX on gear when it's serving a purpose for 2 different jobs.

Them going back and adding DEX to previous gear is a lot simpler than re-balancing MNK. All they have to do is take whatever the STR value is and copy+paste it for DEX.