Heh. It always makes me giggle when someone tries to claim simplicity in AD&D.
Simple scenario. 3rd level fighter in chainmail and shield armed with a longsword is being attacked by three orcs - 2 in leather armor, one in chainmail, one armed with a spear, one with a morning star and one with a longsword. They are fighting on uneven ground with hillocks.
How many steps do you have to go through to calculate what each of those orcs need to hit that fighter?
1. Each orc needs to consult the weapon vs armor table - as each one is armed with a different weapon and will have a different modifier.
2. The target number of each orc will change depending on the order that you roll the attacks as the fighter's shield will only work against a certain number of orcs. Note, we need more information about the fighter's shield because at this point we can't actually answer how many attacks will be affected by the shield.
3. Despite a system that claims not to need to use minis, we need the exact positioning of each orc to know if any of them are at a higher elevation than the fighter.
4. We also need to know the exact positioning of the orcs since the space/reach of each weapon is different, meaning that we don't actually know whether or not all three orcs could attack the fighter.
Now, let's do the same set up for 4e.
Fighter has an AC of X. Orcs have an attack bonus of Y. Their target number is X-Y. Done.