I'll come in on the roster question, as I'd like to think I know a little about this subject.
I'll first address the fallacy:
"People slowly but inexorably rank up"
The main reason why the roster never becomes top heavy is that rank is by no means a metric of time spent, especially the higher up the ranks you go. The simple abilities to lead and multitask are not qualities that every player will have when they come to the server. Some people are not capable of learning these skills either from our tuition, which while disappointing, means NCOship is not a path meant for them.
Additionally, the higher up the ranks you go, the more you will be required to be involved with the faction at an OOC level. Ask any sergeant. They've been asked to drop what they're doing because they're needed and get on the server numerous times. Simply, you'll have commitments that you're expected to meet.
These two points combine, so that only those who are both able to lead AND willing to commit extend periods of time will rise through the ranks.
Now to ensure that its not a pure chaos engine, the command staff spend countless hours discussing those who are promotion worthy. This ensures that the NCO pool reflects our player base size accurately.
As to:
PK's are the least common way to lose a high ranking NCO. This is because we vet our NCOs up to this point, to avoid such foolhardy deaths. Its more common that real life robs us of the player's time, so they can't be active enough to justify holding the rank.
A further note, to all those who gripe at the number of lance corporals, these are the most common military paygrades from 2013, with the study being conducted by the military times:
(http://forums.militarytimes.com/showthread.php/6857-Distribution-of-Enlisted-Ranks)
Army E-4 (30.76%)
Navy E-5 (23.13%)
Marines E-3 (27.62%)
Air Force E-5 (25.5%)
Lance corporals (marines) and specialist/corporals (army) are the most common ranks in the modern US military, which while not perfect, is a good base to model from.
If you want me to explain why this is, or why it's acceptable for SST to ever reach these distributions (N.B. we don't, grades E1 and E2 individually far outweigh our numbers for E3 - E7 combined), then I can.
As a final note, it's not an admins job to PK people to ensure the roster remains bottom heavy. PKs should only be handed to those worthy of permadeath, not under some ludicrous idea of "letting others rise up".