This from The Fielding Bible:
"The thing with him is that he’s horrible but in a balanced way. A lot of players will be really bad at balls hit to their right or balls hit to their left. Hosmer, however, is bad overall. In 2011, he’s -6 on balls hit to his right, -6 on balls hit right to him, and -5 on balls hit to his left. Hosmer is also bad at fielding bunts (-2 runs saved last year). Sounds like a case of people not wanting to hear that players on their favorite team aren’t that good (see: Jeter, Derek)."
If I could explain his answer, BIS tracks all first basemen (as well as the players at other positions) on a set criteria. In this case they will measure how a player does in fielding to his right, left, at him, and in front of him. I think what's happening in his case is that since he is balanced defensively he appears to be good. Often we notice badness when we see either a lot of errors or we see that a player consistently cannot make a particular play.
The problem with evaluating fielders is that generally speaking we notice the superior and the butchers. Hosmer is neither. He is simply challenged when it comes to range. I believe that he has good hands and that he makes the plays he is supposed to make. Most ML players do that. Unfortunately, we do not see what other first basemen are doing enough to be impartial. When I was younger, I would have sworn that Jeff Bagwell was superior before he had shoulder problems. I saw him play everyday. The truth was that he was good, but not great. I didn't get to see J,T, Snow, Mark Grace, or the other great first basemen play more than 15-20 times a season.
Coaches and scouts will tell you that the ML game is a lot faster than it is in the minors. It may be a case that Hosmer was superior in the minors, but needs time to adjust to the quicker game. It could be a case of trusting his instincts and going on reaction. It could be simply learning what he can and can't do with those around him. So, he is not condemned to a life of being a subpar first baseman. Scouts that say he will be great may very well be right. He just wasn't good this past season."
I got this quote indirectly thru an article in The Bleacher Report written by Scott Barzilla on the "Royals Offseason Fielding Breakdown in 2011". In the article, he rated Hoz as the worst defender on the team based on 4 leading "metric" systems. The responses were unanimously in protest of this aspect of the article (It was not all about Hosmer), which lead Barzilla, himself not a specific KC fan, to contact The Fielding Bible for a better explanation. If nothing else, its interesting: