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.
A resume is an important tool, but it can't get you a job. Only people can do that. If you want your job search to be successful, concentrate on people and prepare your resume to suit their needs.