If you place whole strawberries into a dry measuring cup, you obviously won't get an accurate measurment of the volume taken up in the cup. The is air between each berry. However, when you place a solid, that has some of the properties of a fluid, i.e. flour, cornstarch, rice, etc, with very small granules, there is minimal space between the particles. It fills the cup. When you overfill the dry measuring cup, and then scrape the top to make the contents level with the rim of the cup, you have an accurate measurement, or at least a pretty close measurement. The only way to achieve a very accurate dry measure is by weight, as there is still air in lighter dry ingredients, such as flour. If you jiggle the dry measure cup, or tap it lightly on a hard surface, after filling it with sifted flour, you will see the contents tack together, or settle, and not completely fill the cup anymore.
But I think we are splitting hairs here. And I'm glad that all this was done with a bit of dry humor. I reinforces my position that this is the best site for cooking on the WWW.
Seeeeeeya; Chief Longwind of the North