Correct, if by 'article content' you mean what is returned by the article command.  So I think it is necessary to be able to get bytes for two commands: article and body.  Then for symmetry it should also be possible to get bytes from the head command.  (It is actually possible for headers to include 8bit data, but it is a violation of the RFC and both rare outside of spam and impossible to handle sensibly in most cases...and it may be the case that most if not all nttpservers sanitize such headers, I don't have any experience in that area.)

On the other hand, this tells me that a possible use case I had been wondering about in email is in fact a valid concern: being able to parse a data stream that contains both strings and bytes :(  That is, one might use nntplib in a mode where you pull the headers as text and the body as bytes and want to hand it off to email to build a Message object from those parts.