Adding to dropthesky and stealdragon...
It becomes simple when you look at it this way:
Earth Defense/Offense -> Military = Soul Society Defense/Offense -> Gotei 13
Military Personnel -> Soldier = Gotei 13 personnel -> Shinigami
Military Recruitment = Gotei 13 Recruitment
Traditional Military Weapon -> Gun = Traditional Gotei Weapon -> Zanpakutou
Gun given once youve reached certain skill level -> Zanpakutou given when you reach certain skill level (dont ask me how the sword soul develops/where it comes from)
Earth Assassination Squad -> Seperate from Military = SS Assasination Squad -> seperate from Gotei (Assasins and soldiers learn completely different things, it would be retarded to group em together neway)
Earth medical force -> part of the military = SS ...you get the f*ckin point...
(soldiers get hurt more than assassins...so medics are grouped with soldiers; assassins are to kill without being detected...seldom do they come under - unless you are Jason Bourne)
A shinigami is one of the many jobs u can obtain in SS. You are special because you are part of the army, you are no longer a citizen. If you are really really really skilled you can try out for the assasination squad. (ive not seen any of them with zanpakutous except soi fon). If that doesn't suit u, u can also become a scientist for the Tech Development Bureau or go into politics and remain in the dead center of Seireitei.
Not only shinigami reside in SS. Get it right. Get it now.
Speaking of politicians and shinigami...i wonder what George Bush's bankai would look like...
Aizen is gangsta for making everyone wear white.
Tousen: "So what are we going to wear anyway? how do we tell each other apart from the shinigami?"
Aizen: "I GOT IT....lets wear exactly what they wear...but make it WHITE!"
Ichimaru: "OH SH*T, now THATS gangsta!"
Tousen: "....even I wouldn't say that..."
Aizen: "Loosen up Tousen...check this out...lets show him Gin!"
Tousen: "... 0_0 ..."