Its not the gameplay, its the justification through setting and story that matters. If you have read the background and the technology depicted in Mass Effect it makes sense to have the weaponry have unlimited ammunition. However with Alpha Protocol, a setting that does not use such advance technology and more on par of current tech, it makes sense for the game not use unlimited ammunition.
It does not come down to realism, Nick. In fact the only one who brought up realism is you. Loser.
It all comes down to the game's setting and background.