What some people tend to forget is that weapons are not sold in only one configuration. It's just like cars. You can buy a car with the base sound system or with the huge 1000W system. You can have your car in blue, black, red, puke-green; You can have it with a nice sleek look or with an ugly wing that creates more drag then anything else. You can pretty much have what you want.
When an army signs a contract for a weapon system, they can also have what ever they want. Do they want their M16A4 with side, top and bottom rails? They will get it. Do they want the M16A4 with the "old-style" M16A1 look? They will. Same goes with the M203 and the way it is attached. It might also depend on where and by whom the weapon will be fabricated. By Colt? By another company licensing the design?
Bottom line is that when you order 1M Unit of a rifle, what ever you ask you will get. There is not just one unique model of M16A4 that exist. Especially considering that most parts of a rifle can be replaced for optional parts. Just like with a car
It's like saying "hey! your car isn't what you say it is... here, I found a picture of a your car on Ze Interweb... it should look like that, so yours is wrong".
That's really amusing.
