Anybody with any experience that requires planning will tell you that nothing ever goes according to plan. EVER. In American football you can never accurately guess what the defense is going to do until seconds before the play when you are already on the ball. This is when all the players (in all positions) adjust and coordinate their blocking and route patterns with each other right up until the ball is snapped to ensure that the play will still be successful. The quarterback may even see something that was missed when the play was called and call a completely different play at the last second. At that point the previous process starts all over again. To say each person has one job is over-simplifying and somewhat ignorant. It's not necessarily a bad thing, just educate yourself before you talk so matter-of-factly.

Edit: Madden is a horrible example of playing American Football in tactics and player ability.