Sometimes a cover just doesn't work, or a new publisher buys the book. Then a new cover is given, and the book gets a new look.
In the case of the Argentine Lover, the publisher took the cover I designed as a filler for my website when the book was released earlier than expected. But two years later, they surprised me with a brand new, very lovely and evocative cover.
Authors rarely get any say in their covers, but the e-book publishers usually make an effort to ask the author what their dream cover would look like. We get to fill out a cover sheet, and make a list of things we like. But I like surprises, so I usually say, 'Do what you think is best!' and send in an excerpt to give the artist a feel for the book.
Notice that Virtual Murder and Ice Man have three different covers!