Detection of Evil and/or Good: "It is important to make a distinction between character alignment and some powerful force of evil or good when this detection function is considered. In general, only a
know alignment spell will determine the evil or good a character holds within. It must be a great evil or a strong good to be detected." (
Dungeon Masters Guide, 1st edition, page 60)
The alignment scheme in 4e is sort of like that in the original D&D set. That had Lawful, Neutral and Chaotic as the main stances; Anti-Clerics additionally were Evil, and Evil High Priests were Chaotic and Evil (Patriarch-level Clerics being Lawful and non-Evil).
"You, as Dungeon Master, must establish the meanings and boundaries of law and order as opposed to chaos and anarchy, as well as the divisions between right and good as opposed to hurtful and evil." (
DMG, 1st ed., p. 24)
As RC noted, the old spell-casting methods did not presume a certain number of encounters per day. "If someone has the ability to cast 3 spells a day, they are unlikely to be able to survive even two battles in a day" is an utterly bizarre notion.
Between what was actually changed in 3e and how people came to mistake their house rules for The Way It Is, a lot of things got a bit askew. That said, I think the "balance" reasoning behind the powers system is pretty clear.
What reason did it have to exist in a game about killing things and taking their stuff, while saving the world from evil?
Yes, the project apparently was all about producing "a game about" those and other things this set of designers had in mind. That is not to my mind the same as producing a revised edition of the
Dungeons & Dragons rules set.