Ok, assume you're right for a moment. I don't think you are, although I do believe it's a very nasty concept having those large corporations so close to the decision making, I'm not willing to put it into the terms you just did. But for argument's sake.
Doesn't the intention and motivators of the soldier play any role here? A soldier who joined the army for the love of his country, for the desire to fight terrorism, for an urge to give his life meaning even, by definition cannot be a mercenary. A good way to check that is wondering if they'd fight for 'the other side' if it paid the same. I think you'll find very few US soldiers willing to fight for anything but the United States.
edit: I saw that this originated with Phrossack's post. Same question to him. I guess the difference might be: soldiers who were called mercenaries, and those who fit the textbook definition.
I don't really regard American soldiers as mercenaries; the majority of them seem motivated primarily by ideological reasons, but people rarely join for just one reason; some like the benefits, or might want military service because they think it will make them better people. I like the fact that American soldiers tend to be more interested in helping than in making money. I like that the US Military is under strong civilian control and has never even attempted to mount a coup.
My point was that the line between merc and soldier can get awfully blurry at times. A mercenary cannot merely be defined as one who fights for money; after all, soldiers fight and they receive money. You might say that mercs, unlike soldiers, fight
mainly for money, but this is difficult to prove. Some mercenaries are motivated by a variety of causes; during its war, Rhodesia employed a great deal of foreigners. They received the same pay as Rhodesian slodiers and for the most part were treated the same way. Many of these foreigners seem to have been ideologically motivated and believed they were fighting for a cause. And maybe some of the Flying Tigers fought in part because they didn't like the idea of Japan invading China and slaughtering millions. Just because these causes were not that of their homelands shouldn't really change anything.
On the other hand, many soldiers throughout time and space have fought for other causes than their "countries". A great deal of soldiers in other times and other places were (or are) poor and needed the money. For example, the majority of Rhodesian soldiers during the Bush War were actually black, and it's hard to imagine them fighting because they liked the idea of white supremacy. And what makes those who fight for nationalistic ideology morally superior to all other soldiers? Would you call a man noble if he signed up for the US Army in 1898 to fight the Spanish? Or what about a Briton at around the same time who wanted to join the fray against the Boers? These wars were not essentially defensive in nature for the US and UK; they were wars of choice and, to a certain extent, greed, declared by government officials. How is it noble to kill strangers because your government tells you to?
I'm not saying military service is morally wrong, either. Far from it. An Iranian who signed up to help stop Saddam's invasion force does seem to be fighting for a good cause. As does an American who joins the Army with the intention of fighting al-Qaeda because his family member died on 9/11. I'm just saying that many soldiers have been or are motivated by pay, that sometimes mercenaries have motives other than money, and that sometimes, even soldiers who intend to "fight for their country" are actually just serving in an unnecessary offensive war started by government officials.