Ok, here is what I think, not weapon wise, but story wise, see the 14th member was used as a backup plan for the organization XIII. See what Xehanort did was he searched for a 14th member for the safety of the Org, he wanted to make sure they could all come back, if they were ever defeted, so what he did was he put the 14th member to sleep, and not to worry the outsiders (sora riku ect.) he still called them Org. XIII. So the 14th member will awake and restore the Org. IF ever member was defeted, but since Roxas wasn't...TA DA!!! So, the Org. was screwed over by Roxas!GOO Roxas!