Why doesn R GUI support keyboard shortcut XYZ ?
The R.app GUI uses Apple frameworks for text editing and thus the behavior of text views (console, editor, etc.) is consistent with other applications and allows a very flexible customization. For example if you are not satistied with the default Emacs-like key bindings that Mac OS X provides, Apple allows you to extend them arbitrarily. For more details see Apple’s documentaton on Key Bindings.