The developers are always supplied with the latest unreal codebase. Depending on the development cycle, new features are either incorporated into their title or ignored.
OFP2 will kick ass! There still is no game that compares to the scope of vehicles and weapons and freedom of movement. No other game makes commanding up to 12 troops in first person so easy. And no other game provides a more realistic simulation of war given all of the above.
Americas Army and Ghost Recon are nice, but deal with only a fraction of the scope of OFP. And since OFP2 will take place during Vietnam era, this should blow all of the others out of the water.. we will see, but the track record is very promising.