Usability implies purpose and audience.
The original audiences were heavily weighted in favor of academics with high levels of computer savvy. Early users were fault tolerant of unsophisticated interface design, satisfied with an absence of pictures, and happy in a world of keystrokes that could flow between the Internet and simple text editors. Content was understood to be information, not entertainment in the mode of the visual arts. And, the Web was not viewed as a comprehensive replacement for the card catalogue in the Library of Congress with a full text search. In current design polemics, this tension seems to exist.