This concept is not exactly stolen from John Hollinger, but it's always nice to have him on your side. Actually, it's hard to break down the exact misdistribution of minutes by the Hawks in a comparative sense. It's hard to just look at the players involved because there's a team concept. For example, Al Horford's peer group for this year (and it's very early yet for drawing big conclusions) looks something like this:
That list just represents my own very rough cut of players who play approximately the same position as Horford and have a similar impact in terms of rebound percentage, scoring efficiency, win shares per 48 minutes, and usage, so I'll admit that it is very unscientific. You can check the links yourself to view the similarities in the advanced stats. If I were put this in a spreadsheet format (and I'm too lazy for that), Horford's minutes would not stand out in any appreciable manner.
It's when you start getting beyond the surface and into context that it looks curious. Among the above, Tim Duncan's minutes are limited because he's an older player in his 14th season. Emeka Okafor's minutes are limited because he has a history of knee problems. Dwight Howard's minutes are slightly suppressed for two separate reasons, the first being his team's tendency to blow out opponents, the second being excellent depth-that depth being displayed by the fact that Brandon Bass is also on this list as a back-up (thereby explaining why his minutes are suppressed).
Take those out, and Horford's low minute tally is more anomalous. And contextually, there isn't an explanation. He's young, he's got almost no injury history to speak of. He's shown very little evidence of becoming less effective when carrying larger loads of minutes. He doesn't foul at an abnormally high rate. He doesn't play for a team with very much frontcourt depth. He and Kevin Love share this mysterious lack of playing time.
Horford isn't just the Hawks' best player to date (just look here at PER, WS/48, and TS% if you disagree with that sentiment) he's arguably among the best in the league right now. The Hawks need to stretch him out a bit more.