[Radek]

It's a tradition from the times when AD&D were desk games instead of computer games. You are right with the untold. Mages in AD&D are parodies to mages as we know them from other games. They have always memorized spells which they do not need and they cannot cast spells awfully needed under given circumstances. The "mana concept" is far better than the "AD&D concept" in any direction as far as computer games are considered. But implementing the "mana concept" results in creating a non AD&D game.