I don't agree. Nothing wrong with spreading out responsibility amongst the playing group. That is how the coach sees it and it is how the coach managed the same player at the Reds.
Calling the lineouts is a huge responsibility, and I might be wrong, but it has always seemed to be the province of the leading lock. Martin Johnson, John Eales, Victor Matfield, etc. Horwill was not calling the lineouts under Deans, either. That might be where I got the idea that he does not want the responsibility. But I think you will find that it is fairly common knowledge that he does not want it.
The player who was developed into a lineout caller is frequently in the starting 15 partnering him at lock. Then there is Mowen also who is currently doing the job.
Mowen has been calling the lineouts all season for the Wobbs.
We don't need Horwill calling lineouts and we have heard from Scott Allan in the past that he is more than capable should it be required, but clearly it isn't. I don't get where you got the idea of him not being willing. Was this a telepathic insight or did you read the tea leaves? The issue revolves around the coaches will, not the players will.
And you, telepathically, know that Horwill is actually willing to call them? Or was that the tea leaves?
Under your logic, why is Sam Whitelock calling the AB lineout rather than Reid or McCaw?
My logic is that one of the locks should call the lineouts, usually the senior lock takes the responsibility, in my limited experience with the game. It is, after all, tactically hugely important in rugby to win your own lineouts, and to put pressure on your opponents. AFAIK, McCaw and Read are not locks. I saw that in my tea leaves.