The Commander specializes in command and social skills. While the fluff write-up heavil.y features the "mustang" style officer (Promoted from within the ranks) The application is pretty obviously the role of an Officer in general. Even the equipment listed is that of a low level Officer from the TT 40k so I'd say the intent was pretty obvious.
I might've been tempted to suggest that specialties may sometimes just denote the relevant experience and/or skills without actually doing anything about a character's position in the hierarchy, but if even the equipment changes then it would indeed seem obvious that it should, by all rights, affect the actual rank of the character.
But as to the topic at hand- what the heck is the basis of separation between Officers and NCOs in 40K? My first instinct is to say 'Schola Progenium education', but there are plenty of Stormtroopers who attended SPs and didn't become Officers. So, if not that, then what...?
I'd actually argue that Schola graduates are the least likely to become officers, simply because there's no regiment for them - except for the Storm Troopers*. In a way, it supports the Grim Darkness™ of the setting that the Imperium's most loyal sons and daughters are the ones exploited the most, in that most of them end up deprived of any chance to rise above their humble orphan origins, instead being assigned to serve as simple cogs in the big machine.
Imperial Guard regiments are raised locally with their officers already in place - by whatever means their original homeworld has assigned them. The entire command structure (sans Commissars) is thus already in place, and on principle, Guard regiments are never reinforced by fresh troops, but instead either fight until they get wiped out, retire, or are merged with another depleted regiment.
The 2E SoB Codex, which goes a bit into detail about the Scholae, does mention that the Navy recruits petty officers out of the Schola, though (filling the gap between the "rabble" press-ganged into service as crew and the noble officers who are too good to deal with said rabble directly), so perhaps the Guard could recruit Schola graduates as NCOs for service in Segmentum Command, where they serve the appointed officers in the staff?
Anyways, as Tygre proposed, I think that the difference between NCOs and Officers really depends on the homeworld, as its culture and military tradition would heavily influence the regiment. Indeed, it is likely that at least some if not most worlds do not even have "non-commissioned officers", as the entire idea of an "officer" that has not actually been "commissioned" as one might be ridiculous to them! (it does sound ridiculous today when you just look at the words)
Certainly, the Roman Legions fared well without this distinction.
So, some worlds could have "NCOs" that are not actually NCOs but simply fulfill their duties, yet count as either enlisted or as officers (depending on how many troops they command), whereas other worlds could have NCOs by current real world definition.
The medieval Sergeant, for example - the origin of the quintessential NCO today - was a simple ranker appointed by the Captain of a company to help him keep order. The term is derived from the Latin "serviens", which means servant. This did not make the Sergeant an NCO, he was still just an enlisted soldier with more authority, like a Corporal.
I believe the distinction later on came as more social classes asserted themselves in-between the simple "peasant or noble", so perhaps whether or not a world has actual NCO-NCOs or not depends on how many classes it has, and how their military leaders may rise to a command position. Lots of opportunities for a GM to get creative - it actually means you have to consider a regiment's homeworld culture!
*: on that note, I've never thought about how promotions in the Storm Trooper regiment would be handled. I guess I could see it two ways - either by promotion through the ranks from the ground up, or by having officers appointed from special nobles (tying into my idea that this formation might be a leftover from the original Terran Imperial Army, explaining its "current" situation that is so utterly different from any other regiment of the Guard) ... or perhaps it could be a mixture of the two, in that most officers are veteran Storm Troopers that somehow actually managed to survive long enough (tricky), yet the overall commanding officer is some noble for whom this is a desk-job position of prestige. With a fancy title like "Lord-Colonel of the Storm Trooper Regiment" ... like today's "General of the Army"?
(sidenote: as always, my interpretations are based solely on GW's original writing - it may well be that they are contradicted in other sources, potentially including FFG's own books which I do not all own myself, so take this with a grain of salt!)
Edited by Lynata, 03 November 2013 - 08:03 AM.