When I'm calculating XP for new monsters using the chart on LL pg 49 I often discover that they don't really line up with very similar monsters in the book. Personally I chalk it up to creative decisions and/or typos.
In a sense, this is why I really dig simpler XP systems. In Star Frontiers you would grant players 1-4 XP when you finished a significant scene. Same with DCC RPG. It leaves XP awards up to the GM, making it much easier to control character advancement. In classic D&D the XP requirements seemed so esoteric to me I just assumed they knew more than I did and rolled with it. And it works, but I like having more of an understanding of the process and more control over it.