Interface is the same. As far as I can see, pretty much all AI issues have been fixed. There was a bug regarding how infantry behaved under artillery fire, but that was fixed in the last patch.
The NATO forces involved, i.e. U.S.Army, USMC, Germans, Canadians and Dutch was based on who was active in Iraq and Afghanistan when the game was designed, i.e. 2005-2007 ish, since it was easy to get info on how the comabt groups were deployed in actual combat operations.
For example, the Canadian Battle Group in CMSF, basically a reinforced infantry battalion, was a carbon copy of the BG deployed to Afghanistan. They also used the Princess Patricia BG because that was the one due to rotate to Afghanistan in mid-2008 and the one most likely to have been involved in the fictional invasion of Syria.
re: the Germans. Part of the reason they were chosen is because everyone loves to play with German forces. It's a holdover from WW2 games. They also have some cool equipment!
I was a beta tester on both CMSF1 and CMSF2 so have a lot of hours in that game.