My dog/cat doesn't go outside very often, and doesn't eat dead things. He/She shouldn't have worms, and doesn't need to be dewormed.
It's very true that dead things do carry worms and such. But, worms and eggs are transmitted by more than just dead things. Grass and plants, flies and bugs, and other dog's environment (i.e. bedding, toys, etc.) can be carriers of the eggs. Even though we are at high education, we DO have roundworms and tapeworms. We recommend deworming your pet twice yearly, spring and fall, with a dewormer that covers both types of worms. We sell the dewormer here in the hospital.