[quote=chukklehed]
Her father was a weapon, remember? She was the child of Spirit (A Death Scythe) and the woman who I learned the name of once but forgot (A Meister). Therefore she has Meister blood from her mother and Weapon blood from her father, allowing her to fill either roll. Since something like that hadn't happened before, they assumed Maka could only be a Meister since her weapon blood was dormant.
[/quote]

I'm definitely with Cirus on this one. The reason she became a Meister was because she never showed any ability or potential to transform, and in the manga it stayed that way. The whole Maka-is-also-a-Weapon thing just came out at the very end of the anime because... Well, I actually don't know. I don't know why they ended the anime there at all. It seemed like an odd choice.