Most game designers understand that the act of play is an act of learning, and learning new things is exactly what makes games interesting. However, different games assume that you get to learn some things in that manner, and other things are just a neccessary alphabet that you have to get as fast as you can to get things up and running.

In a classical example, you can spend your whole life learning chess, but no one expects you to figure out how different pieces move by trial and error - it's explained prior to the game. It's not because chess game designers are lazy: it's because figuring out how pieces move wouldn't be a fun gameplay.