What is the reason for partially allowing visibility control of linked objects in the outliner? When I link an object from another file, the visibility, selectability and renderability icons in the outliner are greyed out and inoperable.  Yet I can control these functions by right-clicking in the outliner or by using hotkeys.

This behavior is different from linking groups where the outliner buttons are fully functional.

Is there some rationale for this partial functionality in the outliner for linked objects (as opposed to linked groups)?  I.e. bug or feature?

(Blender 2.77a, Windows 10 64-bit)
When you link objects the linked object reflects the object in another .blend file. It wouldn't make sense for user to seem to be able to make changes to it.

When you link groups you are not really linking the objects themselves, but a new instance of the collection of objects. Its the same as when operating within the same .blend: new instance of object can be manipulated without affecting the original copies as long as you don't manipulate the data ie. mesh itself for mesh objects.