There is a difference, though to the average passenger it is not apparent, and made worse since some airlines like Southwest use the term Ticketless Travel when they are really using E-Tickets.
With an e-ticket, the usual paper ticket data, including a ticket number, is generated, but rather than being printed onto paper, the information is instead loaded into the reservation in what is called the ETR (E-Ticket Record).
Ticketless travel, on the other hand, generates no ticket information at all, all that is needed to the airline is a record that the reservation is paid for. Some travel agencies, particularly those that are highly automated, can't handle this, so instead a paper ticket is generated; the ticket number is inserted into the reservation and the airline accepts that, along with the paper tickets presented by the passenger at check-in, as proof of payment. This is why you will get paper tickets from sites like Cheap Tickets, for ticketless travel airlines like AirTran and Spirit.
Southwest does e-tickets; if you look on your "Ticketless Travel" receipt, you will see a ticket number. Or at least, they did in 2000, the last time I flew WN
. Southwest's ARC number is 526.
David / MRY