I don't mean to knock cinema representation of warfare, per seI think it is as valid in an artistic sense as the pre WWI paintings of battles, and in fact derives from that tradition. The object of the exercise is to depict a totality in a way which tells a story and makes a point. To be successful it also has to entertain, in its broadest sense. To achieve these aims it must at some point abandon reality, since the one thing which is common to all participants is a total lack of any sense of what is going on around them or the overall picture. As many have pointed out, the thing that amazes most about the reality of a battle is the emptiness.
So I can accept that a film maker may re-create a given scene accurately for his "placement" shots, but I don't think this should be taken as an indication of the veracity of the film as history. For the film to be cohesive artistically, let alone comprehensible to an audience, liberties have to be taken.
One of the reasons I think this is an important subject is the apparent growing tendency of the general public to swallow entertainment as fact. Apart from the anachronism of the tune mentioned above, which I am sure is now "recognised" as a US civil war tune by the majority of the US population, we have seen examples in other threads of folk song being taken as accurate history! I think this is worrying trend from both an artistic and historic point of view, both of which fields interest me.