[quote=Blitz]
Riku has a Keyblade. (Which confuses me because Sora's Keyblade is supposed to be Riku's... but whatever.)
[/quote]

I think that it could be argued that since Riku gave his heart to darkness, he lost the opportunity to wield that particular Keyblade, but, thanks to Ansem/Xehanort's influence, as well as his deeds in COM and KHII (and trapping himself in the Realm of Darkness in KHI), allowed him the opportunity to use the Keyblade again, even if it's not the Key to the World's Hearts :T