Exclusives?

Are multiple submissions unethical? It's unethical for a magazine or book publisher to hang on to your manuscript/story for months, sometimes years-sometimes knows an the "exclusive." Fear not the shotgun approach--the chances of two publishers accepting your work at same time are astronomical. I accumulated 250 short story rejection slips before I began to sell anything. So did many authors, who are brand names today. Hint: personalize each query for each agent/publisher. Don't get over-familiar or explain your aspirations, hopes and dreams. State the facts. This is a business.