Yea it really is made that way. Only the tools developers have vs the modders and map makers is a lot more complex and advanced level. Obviously it isn't that simple, but for a talented developer that has a single person assigned to a different task, it isn't that difficult to populate an area with enemies and assign them some level of scripting. The AI has already been programmed into the game, so that doesn't need any changing. Enemies will duck in and out of cover, try to flank you, etc. That's already in the game.