There is some sort of momentum modifier in there somewhere that hasn't really been quantified yet though. Fumbles on ensuing kick offs after a big play (pick six, fumble return for TD, etc.) when you are losing are a pretty common occurrence. Maybe a relic of the old hot and cold system, but there is something there that may make people think the game is "predetermined" because of those large swings.
Also, as we found out this year, through the away team fatigue bug there is a home field advantage that we don't fully understand but is definitely noticeable at times.