Gnostic, it seems a little at odds to state Vickerman was quite as useless* and ineffective as you say, especially when one looks at Scott Allen's excellent front page piece on the involvement rates for Wallaby players.
http://www.greenandgoldrugby.com/wallabies-2011-involvement-rates/
Now, I don't want to have a debate about the methodology of how those figures were generated (mainly because I don't fully understand it all!!), but it seems he was doing quite a lot.
I accept firstly you don't particularly like him, nor the fact that he got "an easy ride" back into the Wallabies, but the fact is he seemed to be far from useless*. Granted he was used more as an impact player, so could go harder for his time there, which may skew things a little.
I would not advocate him starting for the Wallabies, unless it was planned to really only use him for 40-50 minutes - I think he is better at the other end. And I wouldn't call him the premier lock either.
But if Horwill is to be the "premier" lock, I think the issue of him assuming more responsibility at Provincial and Test level with regard to lineouts needs to be addressed. I mean, he is the only sure pick, and is likely to play most, if not all, the game. Better it is him than someone who's going to be subbed.
*= me paraphrasing