Maybe it's just me, but it seems like Mac OS knows where a file is even when it's moved. Does anybody know why this is?
In addition to the file's path, Mac OS aliases record several pieces of additional information: the file's unique ID, its parent directory ID, file size, [possibly creation time]; which are used to locate the most probable match in case of a broken link. I think most of the time a file is found by its unique ID, which does not change after a rename.
See also Alias (Mac OS) on Wikipedia.
So it knows what to expect in a place, knows of another way to refer to it, looks that up and there you go. It's like if someone moved house, you still have their mobile phone number to call.