99.5% of all ripple is still held by Developers of Ripple.
Sounds pretty centralized to me.
XRP is an infrastructure component. A small amount is destroyed with every transaction, to mitigate issues like DDOS attacks. It will be given away by Ripple Labs to spur adoption.
It is a single (and vital) component of the Ripple system, that supports the decentralized network---and allows for distributed transactions with all other currencies. XRP != Ripple. Ripple's decentralized benefits are (partially) enabled through it.
Note: while XRP cannot be mined, Ripple has undertaken an initiative to support the World Community Grid---similar to CureCoin and GridCoin:
https://www.computingforgood.org/Ripple Labs is highly focused on distributing XRP, and has found a way to promote a great cause in turn.