I get what you are saying, why aren't all the maps populated? I would (pulled from my butt) say they just left that stuff out because it doesn't really take up that much memory (compared to graphical maps), and easy to add the code later. Maybe the enemies would just be chillin taking up server capacity or something. Funny - my roommate created our college dorm in a HL MP map. Watching him sort of game me the idea that I had a rough idea how games were made.