> A manual should never be needed.

That's going too far.

Also, we're talking about the 8-bit era: 1) technical limits prevented a lot of in-game exposition that you could do now and 2) before the internet, people had fewer options for reading material. I read every manual for every NES and SNES game I ever had, multiple times. If I was into a game my options were limited to 1) play it, 2) read the manual if I couldn't play it (e.g. if I wasn't at home or not allowed to take over the TV to play).