Assuming you don't cook in excess water then drain it away, there's not a difference in nutritional value here, you're just not comparing the same amount of rice.
Raw, uncooked rice and beans are dry. When you cook them you add water. So if say you start with 100g of raw brown rice, you might end up with 330g of cooked brown rice. If you then take just 100g of it, it'll have less than 1/3 of the original nutritional value - you're basically eating 30g of rice and 70g of water. But if you eat all of it, it'll have the same nutritional value it started with.
Same idea applies if you start with one cup. It expands when you cook it, to perhaps a bit over 3 cups of rice, so if you take one cup to eat, it's just less rice.
The ratios of cooked weight to raw weight, and cooked volume to raw volume, depend a bit on exactly how you cook the rice. The nutrition facts are based on some average of "properly" cooked rice.
If you do cook things in excess water, then yes, there is some very small amount of nutrients in the water (it's still water, not a protein shake), hard to say exactly how much, and if you're determined to get every last bit of nutrition you can eat it. For rice it's generally a non-issue, since you don't need excess water - just use the right amount and it'll all boil away or be absorbed. Beans are generally cooked with a bit of excess water, but they don't need an insane amount, so it's not hard to turn that into a soup/sauce for the beans, and so there's still nothing to throw out.