I'm a former British soldier and currently a Firearms Officer in the Police. The kneeling/standing question is quite interesting. In a controlled environment the kneeling position will always be more accurate than standing, however, there are so many variables in reality that make this statement false. Type of weapon, situation, extra weight/balance issues, fitness etc etc. In the Military your role is more defined, it's all about cover, control, and maximizing your chances and minimizing the dangers. Therefore a lot of firing will be done supported (By cover etc) regardless of your stance. In the Police, rarely do you kneel (Even though it has a little part in the qualification) as the role is different. It's about resolving an outcome and most of the shooting is done stood, purely because movement is key a lot of the time.
Of course, I am generalising a lot here. What I'm trying to say is, kneeling doesn't always mean more accurate in reality. It may do on the range (Although in my experience a lot of people's accuracy suffered on the range too) but in reality it can be very different.
:)