It's like they had to for Xion's sake, though wouldn't she also find it suspicious that she doesn't have a pillar or PoE assuming she and Roxas don't share one? \o/ She probably does lol.
Unless, you know, she was already aware of her true 'status' as a member. It would serve to explain why she said that without the Keyblade, she's useless.
Yes, Xion has combat abilities and unless Namine could do what the pic in her FC I posted has her doing, Namine doesn't have them.
Then why are you arguing, if you agree!? D:<