I think the idea of encapsulation is that you only need to concern yourself with the object's interface, and not worry yourself about what's going on inside. (Especially since closed-source development can mean you don't get to see what's inside!)
The onus is then on the class's author to write decent documentation that tells you exactly how to use said interface without having to peer at the code to figure out what it does.
But that said, some people do seem to go overboard: it gets especially silly in a runtime-compiled language like PHP (in something like C++ it all boils down to machine code and memory addresses anyway, and most compilers these days are pretty good at resolving all the layers of indirection involved). And when you've got dozens of classes all building on each other in seemingly trivial ways you're left asking "But which one do I use?!"
