I wonder if we originally only had UnicodeError and it got split later but these codecs were never updated.  The codecs date back to the start of unicode support in python2, I think.

Adding MAL, he's likely to have an opinion on this ;)

Oh, right.  The more likely possibility is that there was (in python2) no way to know if the operation was (from the user's POV) encoding or decoding when the codec was called.  In python3 we do know, when the codec is called via encode/decode, but the codecs are still generic in principle.  So yeah, we need MAL's opinion.  (Or, I could be completely confused, since I always found encode/decode confusing in python2 :)