This is my take on why KM's context menu is designed as such. I believe Peter has made a prudent choice using the DRY (Don't Repeat Yourself) and KISS (Keep It Simply Simple: for nicer word of it :} ) principle . That said, UI design is both art and science.
Those commands (Copy,Delete, Paste) that you mention already serve by those item under Edit menu as as shown in picture
So those operations can be consistently applied to item under selection (eg text, action, macro, macrogroup). Generally efficient users will prefer to use shorcut key to perform common operations (afterall these are standard shortcut key for these operations so they expect it to work that way in KM) instead of menu. Hence there is no reason to repeat it in context menu.
The context menu for the action hence only shown other functions specifically for it. As for why those "Copy as" items are duplicated in context menu since they also appear under Edit menu. These are for convenience and discoverability reason.
As for rename, users are likely to perform selection more than renaming upon clicking on the action title area. In practice, users don't frequently rename actions unless those require special attention and clarification. Hence it may annoy users who expect the action to be selected end up in renaming mode.