the missile launcher is actually a part of the arm, as an integrated weapon.
some info From Software announced today:
-back weapon is gone, replaced by swapping hand weapon.(back weapon are not listed as available customize option. Seraphic was right after all)
-weapon can be discarded like previous game.
-you can put missile, rocket, etc into shoulder. these are call Shoulder unit.
-added new Recon Unit. exactly as what it says on the tin. combine with scanning mode for greater effect.
-there are 3 types of weapon now. KE: kinetic weapon, uses ammunition. CE: chemical weapon, uses chemical ammunition. TE: thermal weapon, uses thermal weapon(i believe flame thrower belong in this category).
-railgun and laser rifle can perform a charge attack. affecting range and damage. consume energy when fired.
-bazooka renamed to battle rifle.
-immobile when deploying weapon and switch to first person view. has higher accuracy and enhance defense with leg shield
-confirmed Glide Boost is similar to Over Boost, can perform a kick attack(i presume this can be done after reaching a certain speed), can boost backward as well.
-High Boost is similar to Quick Boost, high acceleration for a short time.
-wall jump is known as Boost Drive. can be use to gain height. also can use in succession.
-can "drift" when landing, change direction quickly when sliding.(i think this is the drift boost, sounds like quick turn to me)
source here: http://www.4gamer.net/games/103/G010386/20110511019/
correction are appreciated.
the removal of back weapon make sense if you think about it. when you use both back weapon in the past, the hands just dangle there anyway, not like i can shoot 4 weapon at once. this shouldn't change the shooting dynamic too much.
whew, this is one long edit...