Then theres terran.
You build the barracks with your SCV, and start making a marine. Where did that person becoming a marine come from? Was he instantly materialised inside the barracks? Did the SCV build him?
Even if there are humans in the barracks when its built, you can produce hundreds of units from the barracks in a long game. Surely there is not enough room for 100s of people in that one small building.
Same thing goes with factories and starports. Where do these viking pilots come from? Where are all these seige tank drivers entering their machines?
Just a little food for thought.