Most Marines will be using the M16A2's for a long while yet. The M16A4's as an interim replacement/upgrade isn't a certainty. We're just taking some liberty in assuming a possible future outcome for the USMC.
The rifles in the pic are M16A2's, and that's probably all you will see in the current Middle East conflict. I have a Soldier of Fortune magazine from March 2003 showing US Army infantry training in Kuwait, and they all have M16A3's or A4's (flattop + M5 RAS). The captions say: Alpha Company, 2nd Platoon of the 3/15 Infantry Regiment, then: B Company, 3rd Battalion, 15th Infantry with 1st Platoon. They've got PEQ-2A IR aiming devices on the sides, and Aimpoint M68s on many rifles.
As for the addon, the M16A4's are pretty much done, except for doing the lower LODs.
I'm working on a new rifle at the moment, something for the sharpshooters...