A very good point you make is those reference manuals.

I still remember being about 11 years old entering the poke commands to makes sounds on the Vic-20 from the manual supplied. [1]

Without them, it would have been impossible to get such a good incentive to do something other than insert a game and click X to start (as such.)

[1] http://www.bombjack.org/commodore/commodore/VIC-20_Personal_...