:idea:
A thought just popped in my head when I was reading another thread (Not a complete thought, but a thought nevertheless). Keyblades are alive in a sense. The elements which compose life in KH are the Heart, Body, and Soul. Keep this in mind.
So, some of you might be wondering, why does V.A.T's keyblades look different? Because they lack a keychain? Well, that's part of the reason.
We already know that keyblades without keychains are assumably forged by hearts, made evident by Ansem (heartless). That being said, it's only logical to assume that V.A.T's keyblades are created in the same process.
The Heart Unlocker used six pure hearts to create it. Darkness incarnates this blade, giving it a concrete form, ala a body. The individual's soul becomes connected with the keyblade. Same goes for V.A.T, but I'm going to say they used their own hearts to forge their keys. A strong heart forges a strong keyblade.
Now, what is a keychain. For now, let's say that the keychain is a type of heart. You can only accomplish so much without a keychain. Those who wield keys without chains are possibly endangering their well being. In Ven's case, his keyblade snapped... possibly due to a weak heart. With the keychain being introduced, the keyblade officially have a heart of it's own, not relying on the hearts of others.
I'm in the midst of making a theory, here, so this isn't complete. I'm just throwing it out there.