I remember seeing a picture of one that looked exactly like that many, many years ago. As you said, it was designed to make the buttons more accessible for someone who wouldn't be able to reach the standard player panel.
I don't know if it was made by IGT or just a creative slot technician. To the best of my knowledge, the switches are normally open, so these extra switches could just be wired in to the traditional player panel switches in such a way that if either the original or the "extension" button is pressed, the machine would register the signal.