Patents are for processes (how)
Copyrights are for the embodiment (the specific code)
To issue a copyright for the idea would muddle the murky line even further
Patents were supposed to be for non-obvious processes.
I frequently see patents issued for what
was a Manual Process, being patented (or getting a New) because a Computer is now being used or we have a Menu (Lotus vs Borland) at the bottom for control
(That one was overturned, but it severely damaged the company)