Don't get caught up in Aiden's comment, it was tongue in cheek. He didn't mean that Apple hides HFS+ from the user by saying "the filesystem", he was pointing at the fact that Apple tries its hardest to make file management not be based on the old paradigm of files and folders, but rather on librairies (iTunes, iPhoto, etc..). This is based on a lot of people that are non technical and talk about the "filesystem" meaning the folders and files they see in Finder. That's not the filesystems, that's your files. Finder is a file manager application, not a filesystem manager application, but to some people the distinction is quite lost.
They don't know that Finder is simply a userspace application that interacts with a standard API that calls into syscalls in the Kernel to get handles to files, which are managed by a VFS layer (open(), write(), read(), close() are the same syscalls in the kernel for every underlying storage type, no matter its actual filesystem) which then maps the call to the actual filesystem driver depending on which handle received the call.
This is quite all besides the point of the kernel structures being used to actually address userspace queries and map them onto the hardware. And the GUI isn't what abstracts this, it's the userspace/kernel space seperation that does.
The CLUI hides as much detail of the modern OS as a the GUI does. You don't directly manipulation kernel structures, set hardware registers or interfere with the process scheduler on the CLUI you know. You interact with the same abstracted view of it all that the GUI presents, just as a text based format rather than with shiny icons.
