Executive search firms need a good resume from you, but they also must have a search assignment that matches your background before they can be of service. Headhunters do not market you. They find the best candidates for client job openings. Their clients are companies that pay their fee or retainer. Don't expect a headhunter to make you her number one marketing project. Conducting your search campaign isn't her job, it's yours.
Replying to all resumes would be the polite thing to do, but often it simply isn't practical. If a company receives 200 responses for an ad, or experiences a continual deluge of unsolicited resumes, it would spend an inordinate amount of time sending acknowledgments. If you really want a receipt for your resume, send a stamped, self-addressed postcard asking for one. If you make it easy, the human resources department will comply.
It used to be true that firms preferred to hire employed people because only the deadwood were let go from a company. However, in the past 10 years, corporate mergers and acquisitions, hostile takeovers, and right-sizings have put many highly qualif ied professionals on the street through no fault of their own. Prospective employers are aware of this trend. If you maintain your self-confidence and tell a potential employer what you can do for him, he will consider another firm's loss his gain.