As a Marine I don't understand why Warmachine would be in the Air Force and not a Marine in the comics.   Just because the suit is capable of flight doesn't mean that the best person for the job would be a pilot.  The suit has more weapons that are used in CQC ( close quarters combat ) and not those used in an actual airborne fire fight.  A Marine would have better training in dealing with these weapons and situations that would need them.  Also Marines have pilots and those pilots go through a more rigorous combat training during their boot camp than does the Air Force.  Its just never really made sense to me that he's an Air Force pilot when being a Marine would make the character and the way that the suit is set up and used more believable. 

War Machine being a pilot in the Air Force makes as much sense as him being in any branch of service. He was a pilot in Vietnam who saved Stark and became his friend. it is only specified in the movies that he is a pilot in the Air Force who is the go between for the AF and Stark.   
 
Complaining about him not being a Marine is about as sensible as you identifying with Captain America, a WWII Army corporal, instead of The Punisher who is a Vietnam veteran from the Marine Corps.  It is what it is. If you want a cool Marine read DC for some John Stewart appearances.  

and john stewart doesn't get many dc appearances lol