No, shampoos are detergents, which is a chemist's way of saying they dissolve oils and therefore the other molecules and stuff that are trapped in the oils (like foodstuffs on a dirty plate). In the case of hair, that other stuff will include pollution from the atmosphere, salt from sweat, skin cells, bacteria, bacterial metabolic products (some of which cause odor), etc. Shampoos allow that stuff to be chemically freed and washed away.

The equivalent would be not using dishwashing liquid for your plates after a greasy meal. Hot water and friction can do a lot, but it is an uphill battle. In the case of hair, your method might just be "good enough", though. But I'm sure your hair won't get the "Gee, Your Hair Smells Terrific" response.