To my knowledge, no one has based any of this on preseason results. To me it's not even an issue of this year. I have a much longer view. It's an issue of risk/reward.
There is little risk to giving the rookies a good dose of PT, and since neither Foster or Nesterovic have their best days ahead of them, there aren't many reasons to give Hibbert as much time. The only reason I would put Nesterovic in a position to get major minutes is to feature him for a contending team in need of a back-up center. Otherwise, let his contract expire and reap the cap space.