Actually, Usenet didn't use the Internet for the first 5 years or so, rather, the main transport was an ad hoc network of systems using UUCP dial up telephone transport, and that persisted for another 5-7 years after NNTP came into existence (around 1986), until real Internet access became afordable and the traffic rose to the point when a modem couldn't cope with it any longer. For quite a while, Usenet was transported as batches thru a wide variety of networks, and even airfreighted magnetic tape.
The ARPANET used mailing lists instead, some of them gatewayed to the equivalent newsgroup. (Yea, it was ARPANET back then. Things military were not tolerated as much as today).
Much of Netiquette that seems arbitrary now, (like limiting posting size, not top posting, including enough of the message to create context, and no commercial postings) came from that era, as necessities to keep volume down, allow the thread to make sense (as it took two or three days to get a reply back and sometimes things got lost) and satisfy the restriction on non-comercial use that was imposed on groups that were gatewayed to the ARPANET mail reflectors.
Mark Zenier snipped-for-privacy@eskimo.com Washington State resident