I heard a story once about a fixed wing pilot - He had become discouraged after receiving no replies for years & stopped sending unsolicited resumes to Qantas. When he finally got an interview after applying for an advertised position they asked him why he had stopped sending resumes a few years previously!
Maybe not in all cases, but I'm sure a lot of those companies know who is keen to work for them after seeing the name appear in the resume pile so many times.