The deal with 2e Paladins.

[JonSetanta]

If I recall correctly, you did get XP for researching new spells, as well as making magic items.

As Rogue one gets XP for finding gold and loot.
Not acquiring, finding.

I suppose it was a noble take on an otherwise bad incentive to kill everything for XP, but poorly implemented.
Quests and tasks for levels would have done better.

[Koumei]

There was also one where you would roll a great big pool of dice, then arrange them into groups and no stat could be over 18 using any amount of dice in the pool, so many 16's and 15's were the result.

This has pretty much become the standard way to do it for Rifts: for human characters, roll 32d6, then discard 8 of them, and arrange the rest into groups of 3. Try to get as many 16+ ones as possible so that you get bonus dice, and make Speed the lowest because it seriously never does anything. Even relative to the "doesn't do much" of the stats in general.

Sigma: IIRC, in 1E there was a crazy rule where you got XP equal to the gold (or value) looted. As a result, people went around threatening creatures known to carry big diamonds, basically doing the "Your GP or your HP!" routine.

Then in 2 & 3, they decided it was fundamentally stupid to weld wealth and level together, even though they sort of did it with 3E. And then in 4E, they did a huge amount of coke and said "Hey, let's weld level to wealth!"

[Hey_I_Can_Chan]

I'm aware they didn't get spells every time they leveled up. I'm pretty sure they got one spell of the appropriate level when they gained a new spell level, though. I remember that because one big balancing factor for bards as spellcasters was supposed to be that they never got to learn new spells except through scrolls and wizards did. This is one of those times I wish I hadn't sold my 2e books so I could look it up.

You get one spell per new spell level for free if you're a specialist wizard.

Otherwise, "When your character attains a new level, he may or may not receive new spells. This is up to your DM. He may allow your character to return to his mentor (provided he departed on good terms!) and add a few spells to his book. It may be possible for your character to copy spells from the spell book of another player character (with his permission, of course). Or he may have to wait until he can find a spell book with new spells. How he gets his spells is one of the things your DM decides" (Player's Handbook 108).

Totally not a house rule at all.

[Absentminded_Wizard]

Ah, now I remember why the only generalist mages you ever saw were NPCs (preferably Mordenkainen or Elminster).