Aight, as near as i can tell, it breaks down like this.

(SPOILER)Outside Kingdom Hearts, there is only supposed to be one Keyblade master. Originally this was supposed to be riku, but riku fell to darkness so it was passed on to sora. Sora then "connected his heart" or something along those lines, with Kairi, i suppose allowing her usage of a keyblade due to this connection. Roxas gets his keyblade due to being Sora's Nobody.


Mickey, on the other hand, as they state early on in KHII, Got his keyblade INSIDE kingdom hearts, it's completely independent of the keyblade Sora wields.

Thats as near as i can get to making since of it. then again, if the chain of "hey, you want keyblades? $5 and proof of connection to sora." type handouts continues, were gonna see Yuffie chucking Metal Chocobo's instead of shuriken in KhIII.