Sorry, I completed both games and you are wrong.Sorry, I completed both games and you are wrong. Just draw a map of the areas in question, the possible traversal paths and existing active actors at any point in time and you will see.
See how easy that was?
Maybe it's because UC doesn't stop you playing every five minutes and hit you with a load screen. It's very clear to see exactly how large a MGS4 level is, because you have to watch loading, like in the olden days...