He signed a three year contract last year, after his break-out at the Vuelta. It can be bought out, but it'd be really expensive.
Apparently Wiggo told him to go for the stage, but Froome stayed with him of his own volition. Looked at with that in mind, it doesn't seem to be the cluster-fuck everyone thought initially. Still can't quite figger it, but...
I really think he's looking to the Vuelta this year for a bit of pay-back, and then next year's tour, as it's the 100th anniversary (or 100th tour, can't remember...), Contador will be back, A. Schleck might be healthy and Frank-less and on Astana, and it may be super, super climb-y. Wiggo might find his wings getting clipped in that scenario.