What causes us to associate songs with particular singers?

I was just thinking of how I associate the song As Time Goes By with the version sung by Dooley Wilson in Casablanca. Dooley Wilson is not exactly a household name but he seems to have nailed that one song better than anyone else. Why should that be? And the association works the other way of course. There are certain singers associated with particular songs, like Andy Williams and Moon River and Ethyl Merman and There’s No Business Like Show Business.

Is there a particular match between personality or singing style with a particular song? Might each of us, regardless of our singing ability, have a particular song that best suits us?