Fallout 3s version of the mall is scaled down and with less buildings simply put. But the mall is huge and theres so much in it.
And due to that I couldn't see Fallout's version. For example when I came out of the metro inside the mall I noticed that everything was huge, but it didn't discourage me. We went into some of the museums first so I never got a look at it, and when we were going to the monument I would say something about fallout which would annoy my brother.
Then you get there and see the ticcket vendor, and walk up to it and there is the circle. It seemed to me that the circle in real life would have been the distance from building to building in Fallout 3, then there are also roads going through the width of the area, just making size even more of a problem. Then it takes forever to walk from one end to another.
Also there are the several museum as opposed to each side covered with buildings, so that may have ruined the similarity for me too.