The pilot reported that he aborted a landing due to traffic on the active runway and retracted the landing gear. He stated that on the second approach to land he carried extra power because of the gusty wind conditions, but during the landing flare, he realized that he had failed to extend the landing gear. After he realized that the landing gear was not extended, the pilot added full power; however, the airplane impacted the runway with the landing gear in the retracted position. The pilot stated that he did not follow the checklist and that he did not hear the landing gear warning horn during his approach. When informed that the throttle position to activate the landing gear warning horn was only about 1/2 inch forward of the full aft idle position, the pilot indicated that he had not retarded the throttle that far. The airplane sustained substantial damage to its undercarriage as a result of the abnormal runway contact.