While vitamin content may decline slowly in storage, and while the species we eat may not have such high concentrations of vitamins, these effects are compensated for by the constant availability of fruit in the urban jungle. But some of the domesticated fruits have quite exceptional amounts of vitamin C, if we take vitamin C as a key desirable quality for a fruit. A medium sized tropical guava has 165 mg, and a single medium kiwifruit has 74 mg. Refer to our 'vitamin C content of fruit' page for a list of more than 50 fruits and their vitamin C content and ranking. But to look only at the vitamin C content is to tell only part of the story.
Fruit are very important sources of vitamin A and various carotenes.
Study after study demonstrates the protective effect of fruit. Protective against cancers, protective against cardiovascular disease. But again, this cannot be a surprise. We evolved in an environment with fruiting plants. We are an omnivore.