actually the rank they call Rear Admiral in the game is Commodore, one pip in a box is the insignia for commodore. They are just using the peacetime nomenclature for the rank, which is Rear Admiral (lower half)
Anyone who has watch Star Trek knows that you do not go from Captain, straight to Admiral.
The Rank step between Captain and Admiral that is missing from game play is "Commodore"
Anyone who is a true fan of Trek will support this fact.
En. Lt. Lt-C. Cmdr. Cpt. Commodore. Admiral.
Anyone who is a "True Fan" of Star Trek, knows that in TNG it was said that the rank of Commodore was discontinued. It's quite simple:
O-1 _ Ensign (En) You start at this rank in the tutorial. This is level 1.
O-2 _ Lieutenant Junior Grade (Lt jg) Because of your awesome performance in the tutorial mission, Starfleet decides to leave you as the CO of the little light cruiser that you saved. Since Lt jg is too junior to be the CO of a even a Frigate or Light Cruiser, they decide to promote you from Ensign to Lt. So this rank exists in game (you can even choose this rank as a title and wear the rank pips if you wish)
O-3 _ Lieutenant (Lt) Levels 2 - 10.
O-4 _ Lieutenant Commander (LCdr) Levels 11 - 20.
O-5 _ Commander (Cdr) Levels 21 - 30.
O-6 _ Captain (Capt) Levels 31 - 40.
O-7 _ Rear Admiral (lower half) (RAdm) Levels 41 - 45. (This is the rank that used to be called Commodore)
O-8 _ Rear Admiral (upper half) (RAdm) Presumably this will be levels 46 - 50, once those levels are added in Season Two.
O-9 _ Vice Admiral (VAdm) Several NPC's have this rank. Not available to players in game.
O-10 Admiral (Adm) Several NPC's have this rank. Not available to players in game.
O-11 Fleet Admiral (FAdm) Since only one officer can have this rank at any one time, they would essentially be the Chief of Starfleet Operations. The equivalent of our Chief of Naval Operations, or since Starfleet is the UFP's senior service, probably closer to our Chairman of the Joint Chiefs of Staff.