I could be mis-remembering the article in question, but I think the percentage increase referred to soldiers who fired their weapon (e.g. assault rifle or sidearm) directly at an enemy they could see - meaning that we've become more desensitised to violence over time.

I also recall that snipers are trained by shooting watermelons - the impact of a high velocity round on a watermelon is not too dissimilar to an impact on a human head. Snipers see the carnage in all its gory detail because of their magnified scope so it's necessary to desensitise them in training.

Edit: slo-mo watermelon getting shot: http://www.youtube.com/watch?v=iO3XsZpOiBA