Dry hopping adds aroma. Any flavor gained is negligible - though aroma can certainly add to the perception of flavor.
Hop contributions have more to do with chemical reactions than anything else.
Early boil hop additions add bittering. You tend to get little aroma or flavor from these, as the compounds get broken down by the boil.
Later on in the boil, you get the flavor additions.
At the end of the boil, you get aroma additions. Aroma compunds are delicate and easily broken down by heat, which is why these come at the end.
Dry hopping also gives aroma - the primary purpose of the act. But again, little in the way of flavor.