Funrunna is right. You have to cook some things to make them digestible and palatable. If you overcook some veggies they lose their nutrition into the water. Stews are cooked for a long time to make them "blend" together.
My Mum was a serial veg murderer and now I always steam veggies and try to get them "el dente" (slightly undercooked). Potatoes can only be done el dente if they are new potatoes. A good tip for this is to boil them until underdone and then drain them and stuff a clean tea-towel over them. This causes them to do the final bit with their own steam. (much better for salad potatoes to be served cold).
Jacket potatoes need more cooking as they are usually "old" or stored potatoes.
NB: The tip with the tea-towel is also good for mashed potatoes. Because the last bit of cooking is done in their own steam, it reduces the water content meaning firmer mash or being able to add butter/milk/cream at a greater rate without the mash going watery!