Corn surely has nutritional value. It simply doesn't have the specific nutritional value of vegetables, i.e., various phytochemicals which are available from few if any sources other than vegetables. The category of "vegetables" is so diverse, that different vegetables provide radically different nutritional benefits.
Corn, specifically, is a high calorie nutritional source, for the money and for the amount of cultivated land it takes to grow it. This is a good thing for much of the world, where food is expensive, and cultivatable land is scarce. That characteristic, though, is probably not such a good characteristic, on the average, in the context of a nation like the United States, where a vast majority of people are overweight and there is an abundance of cultivable land.
However, corn also provides a substantial amount of protein, far more than vegetables, and far more per acre of cultivated land than most any other protein source, other than soybeans and other grains. That's really the key differentiator, from a nutritional standpoint, between vegetables and things that we often associate with vegetables, such as grains and legumes. The latter group have substantial amounts of protein, while vegetables do not.