Here are some good links outlining Encapsulation. While they refer to other languages, the ideas are basically the same and would be a good read for anyone trying to understand Encapsulation:
Searching the web for "RPG Encapsulation" will get you some interesting results. Most of them relate to teaching RPG Programmers Java or are focused on complaining about the lack of such things in RPG. And I'm sure it goes without saying that a lot of the results were focused on VB programming for Role-Playing-Games! Still, I was able to find a couple of gems:
I also have two articles published at ITJungle that cover Encapsulation techniques specific to RPG: