You have been lied to your entire life.
A rice cooker can cook more than rice.
Yes, a standard electric rice cooker is designed to bring rice to a boil, sense when it needs to reduce to a simmer, then lower the heat again to keep rice at serving temperature without overcooking it.
That may sound like a very smart little machine, but YOU ARE SMARTER. You can trick the thermostat (just press "Cook" again) and manipulate that nonstick cooking surface to do whatever you want!
In her excellent New York Times piece on the topic, Julia Moskin explains it just right: "Cooking foods other than rice in a rice cooker is like baking a layer cake in an Easy-Bake oven: best approached with patience, curiosity and something to snack on in the meantime."
But it's worth the experimentation, especially for people who don't have a full stove or a large kitchen. Just take it from Roger Ebert (RIP). Put a bunch of ingredients in there and give it a go. Melt a little butter, add onions or shallots, and use it the same way you might a big dutch oven. Know that the heat doesn't get very high. Here are some recipes to try.
1. Tofu And Asparagus
Put the ingredients in, turn on the rice cooker, come back 15 minutes later and you have a meal. Find the recipe here.