Actually the whole idea of the "Apogee Model" was that they took the full game and split it into episodes, to encourage you to want to buy the rest.
Shareware was originally a system where people would basically share full version programs and then expect users to register/pay for it if they continued use, but these were generally small time programs but solo programmers. When Apogee came along, most people switch to their method and programmed in limits to unregistered software or only gave you part of a program.