.
The ability to master the rules plus having detailed references (which are really just distilled rules) doesn't make a game rules light. It just means you've mastered them to the point that you don't need to reference them frequently.
Ah, but I believe you don't NEED to master 4e rules.
Let's say you are a DM and you grab a random monster. If the monster has Improved Grab or Spells, you HAVE to crack open the PHB unless you know those details off in your head (and yes, it is possible to memorize spells)
Contrast that with a 4e DM. Is he going to need the PHB for anything? No. All the monster's info is right there...
I fully admit I never saw a DM screen for 1e or BD&D so I don't know what it contained but I do know from experience that when I DM 2e and 3e, my PHB and Monster manual are both open during the game.