You did notice that US. Riflemen and Officers already have an 4x zoom on their weapons?
At the moment only the ironsights with the zoom are used, real scopes are due in 0.7.
Also,the M4 is not meant to be a weapon for long ranges. It is a carbine with high ROF but low range and accuracy. Furthermore, a reflex sight is usually without or low zoom so that you can look through it with both eyes open without getting a headache. Oh, also it has hardly any zoom because it is
meant for Cose Quarter Battle, but who cares about that as long there could be a risk of headache

.
So, wait until 0.7, there you'll get shiny scopes and (hopefully) reduced recoil on M16 and consorts, so that the Americans will have a chance at high ranges.
And dun't you touch my beloved G3! It stays how it is (ok,maybe with a bit more recoil, but thats it

).
I dearly hope that in 0.7 we will feel the difference between a Battle Rifle (G3), made for long range engagements with high firepower, but lacking CQ capabilities, and Assault Rifles (M16,L85 etc.) which are suited for both situations and thus increasing the different styles of play for each army.