The rice cooker CAN do more than just cook rice (many larger cookers come with a steamer basket that sets on the top of the rice bowl, allowing you to steam veggies or meat while your rice cooks), but if you're the type to own a rice cooker, you will probably use it for that one thing. In college, I used my small rice cooker not only to make rice, but to make pastas, soups, and stir fries in my dorm room, where hot plates were a no-no. You can make steel-cut oats fairly mindlessly over night without using the giant crockpot.
Here's the deal - if you live in an Asian household, you have rice...you have rice COOKED AND READY TO GO AT ALL TIMES. It is not a side, it is the base of every meal. If you have an 8 cup rice cooker, your family of four is all set...for that ONE DAY. (Large rice cookers have a "keep warm" function.) Fire up the cooker to full capacity in the morning, use the rice you need for breakfast...come back to the cooker at lunch, and find the remaining rice still fluffy and warm, waiting for you...come back to it at supper for the last of it, still fluffy and warm.
Yes, you could make it on the stove top, but you have to set the pot to simmer just right, set the timer, make sure the lid doesn't simmer over. And then keeping it warm for long periods of time without burning the bottom (or wasting tons of gas)? Good luck with that. Plug in the rice cooker, put your fingertip on the bottom of the pot, fill to your first knuckle with jasmine rice. (Yes, jasmine rice. You could assert that there are other, better rices to choose from, but you would be wrong.) Fill to your second knuckle with cold water. Close it, flip the switch to COOK, and walk away. When it's done, the cooker will automatically switch to KEEP WARM. It will be fluffy and moist, not soggy, not dry, not crunchy, not browned (if your cooker isn't a crappy one). It will stay that way for over 24 hours, but WHO DOESN'T EAT ALL THAT FRAGRANT, HEAVENLY JASMINE RICE IN A DAY? Oh...right...
If you make rice for only one or two people, for only one or two meals a month? Yeah, you don't need a rice cooker. But to an Asian family, the rice cooker is to us what the coffee pot is to many American homes - an all-day necessity. We will use the whole pot over the whole day, and start over the next day.
Also, if you add butter or soy sauce to your jasmine rice, you deserve a high-five...in the face...with a chair. Jasmine rice needs NOTHING, although if you live on the typical sodium-rich diet that burns out tastebuds like Luke Perry's career post-90210, you may add a splash of nam pla, which is delicate enough to add salt but not overpower the rice's natural flavor.
This has been your token Asian, talking about Asian things, in the most Asian way possible (short of doing it in an Asian language).
*weis, bows*