"There are 3 billion Spanish speakers worldwide"
But then you learned that only 500 million were really fluent, and the rest ranged from broken Spanish that was enough to get by in a Spanish speaking country to people who were forced to take a Spanish class in highschool and never used it again.
I think this concept of "fluency" in games is probably a more useful metric. The question is, if I dump you in front of a game that you've never played before, but it conforms to the language of video game design, how quickly can you beat it? I would imagine that someone who only played Candy Crush would not understand how to move their camera around in a 3D environment, for example.[1]
You could extend the metaphor further, for example Spanish is spoken in many different ways around the globe, and therefore some people who speak one dialect of Spanish can't understand another dialect of Spanish. The same could be true for games, and we would need to classify and understand these dialects.
[1] https://www.youtube.com/watch?v=ax7f3JZJHSw Interesting video talking about what games are like for a non-gamer, shows an example of not understanding how to move the camera and the player at the same time.