The level draining discussion reminds me... in the original boxed set, monster XP was 100 x monster level - where level was either HD, or the next up HD if they had HD+1 or higher. (Like a few other important things in the boxed set, this isn't explained directly - you have to glean it from the example in Book I, page 18.)
In Greyhawk, Gygax changed this to roughly the XP values used for Basic D&D and 1e, which were much much stingier. (Also, you had to calculate these values yourself! Until the 1e DMG was released, anyway.) The rationale: that the original 100 x level amounts were much too generous. Only Gygax could look at a game as lethal as original-boxed-set 0e and think that...
Also of note: XP in 0e (for both monsters and treasure) was multiplied by (higher of current dungeon level or monster level)/(character level). In the aforementioned example, a 8th-level magic-user on the 5th level of a dungeon earns 5/8 of the base XP (but would earn 7/8 for defeating a troll, which counts as level 7.)