As I've previously mentioned, I like how ludology can be applied to other areas of human behavior to make them more entertaining. One of the major ways this notion is currently being utilized is with education.
This post, however, is about bringing knowledge to games, instead of bringing games to knowledge. What do I mean by that. Well, most all games usually require both skill and knowledge. The challenge of these games is in honing ones skills, and acquiring the appropriate knowledge. Often times, WHAT the knowledge is that needs to be acquired, is of little consequence. In these situations I advocate using knowledge that has relevance in the real world, such that the knowledge you are encouraging your players to learn, is information that might benefit your players outside of the game.
This, I believe is different from making an educational game in that, you aren't making a game in the attempts of teaching anyone anything, but if you have to base some of the difficulty off learning, why not have your players learn something useful.
My first example of this is the Desert Eagle. Pretty much all gamers know about the desert eagle, because games like counter strike used real world knowledge in their game. It's rare that knowing what a desert eagle is, helps me in my everyday life, but I think it's quite a pervasive example of a piece of knowledge that would normally be obscure, becoming almost common place as the result of being utilized in a game. Other FPS games with a modern theme have chosen to make-up their own guns, and they could certainly have a creative reason for doing this, but the fact remains that learning about made-up guns has no real-world use, while learning about real guns could.
If you are making a game where a generic helicopter is attacking a player controlled sand-worm, why not call the helicopter by name. If you are making a 'matching like items' puzzle, why not make those items real world items with real-world connections. Instead of filling a skill tree with made-up terms, consider using accurate real world terms. e.g. The word 'stoic' is used for a skill in WoW. Think about how many people learned the word stoic, after playing a WoW paladin.
Instead of making a bland, generic fantasy/sci-fi RTS, make an RTS where real world bacteria fight with one another. Make everyone learn how much more maneuverable your amoebas are when they get the flagella upgrade.
Games are powerful, and are getting more powerful the more mainstream they become. At some point game developers will have to really start taking responsibility for their social impact. While games currently do a great job of entertaining, they can also do quite an excellent job of absorbing time that people could use to be productive. This time-sink nature is a detriment on the order of recreational drugs. People can, and clearly have, wasted their lives playing addicting video games with no real world merit. If we as game developers aren't responsible, and actively look for ways to improve the utility of games at the social level, the reputations of video games in general will continue to decline, until they are widely held to be as bad as drug use.
Adding real-world knowledge to games is one way to increase the utility of games, and while it's not always an option, when it is I highly recommend taking advantage of it.