Simple
EAW is European Air War
UAW is Universal Air War, because as well as having theatres in Europe we have theatres in North Africa, Iraq, the South Pacific, and many other areas that are not in Europe. It is still EAW but with a different name
Some theatres are not "multiplayer friendly" because of the positioning of bases and targets. They are fine offline in that you can do a ground-started mission, skip to waypoints and even accelerate time.
In multiplayer you cannot skip to waypoints or accelerate time. If you fly a ground-started mission and the distances are too far then it would take a ridiculously long time to reach the target or make contact with the enemy.
Hence, some of my installations are "reduced", with only "multiplayer friendly" theatres in the installation. They work well offline too, but they are released for the convenience of online players.