If we were talking about chess pieces, I would absolutely agree with you and mgteich. Take Alexander for instance. Say he is #4 on the ILB depth chart (and even worse if you include Tank and Rodney in the equation) and behind Izzo, Woods, etc. for a ST role, it would be hard to get him gameday active without some kind of injury.
You see an inactive Alexander providing solid depth. I see a 26 year old player in a contract year not getting any game action to improve his skills and demonstrate his abilities for potential future employers. Anyone would think that arrangement sucked and I don't think Belichick would do that to a veteran player. Same for Jordan or Aiken.
That is why I see the 8 inactive spots as needing special consideration for non-developmental players. Telling a veteran player not to dress for a game repeatedly will result in an unhappy player, a sucky locker room presence and likely uneven performances when he does happen to get playing time.
Come week three, the projected camp inactive spots will be meaningless. At that point, there are injuries to players that force the inactives into playing time.
That, combined with varying gameplans and schemes, means that you need the inactives to be fungible and able to replace others. Being inactive one week sucks, but that can change so easily by the next I don't think Belichick would hurt his team's chances of winning because Eric Alexander may be unhappy with his playing time to begin the year.
You can't fill up spots 46-53 with players who are developmental or only useful on special teams - they need to be able to step in and help the offense and defense if need be.