You can do the math yourself. They tell you 60GB, but that's with 1000B = 1KB. In reality, everything is in powers of 2, so 1024B = 1KB. So their 60"GB" = 60x10^9B.
60x10^9B/1024 = 58,593,750KB
above/1024 = 57,220MB
above/1024 = 55.9GB
That's just the way things are. Sorry. The good news is that there's nothing wrong with your drive.