It is crisis in (road) cycling.
Look at all the riders that had a hard time finding a pro-team (if they found one at all)
If Wiggo still has a contract for 1 year, it might just be that Sky is waiting to see what his result(s) will be this year.
If it ain't good they can put a new contract before him with a lot less money on it.
Of course, if he does show flash(es) of his 2012 year, they'll have to pay him more to keep him, but still.. I would understand Sky's way of thinking (if my assumptions would be right)
And since he ain't the youngest either anymore, Sky might just not even be very interested in keeping him all together either and use the money to get a young prospect (e.g. someone like Kelderman, Kwiatkowski, Talansky,...)