I was watching something on tv a couple of months back about MA. They did an interview with the guy that teaches Gracie-JJ in the army. The jist of his comments were that no martial art is really usefull since wars are fought with guns and bombs and whatnot, they teach them for the qualities that they(MA) develop. I think their choice of art is greatly influenced by popular opinion and simplicity of the art.
BJJ is a total art. There is much more to it than just ground fighting. Obviously those who are writing negative things about it know very little about the art and are basing their oppinons on sport juijitsu.
Soldiers need to be tought techniques that are easy to use. They need to be able to fight in any environment, situation and range.
Most combat instructors have experience in several arts. Drawing techniques from aikido, karate, kung fu, JKD, kali, ecrima etc.
Interestingly, when Minoru Mochizuki went to France he was challenged by fencers, savate, wrestlers and boxers. He realized that Daito Ryu Aiki jujitsu was useless. So he changed to judo and kendo techniques and won easily. This is why he has added many judo and karate techniques to aikido. Upon returning to Japan he suggested to Ueshiba that he change aikido but he wasn't interested.