As with all disk or flash based storage, there is a discrepancy between the advertised size and the formatted space available to the user. It has to do with the numbering convention used by manufacturers and the one used by computer operating systems.
Storage manufacturers define prefixes like mega- or giga- in terms of powers of 1000.
Operating systems such as Windows or Linux define these prefixes in powers of 1024.
Newer version of OS X (10.6 and up) define the prefixes in powers or 1000.
A 64 GB drive according to the manufacturer has 64,000,000,000 bytes. When read by the operating system this capacity is interpreted as 64,000,000,000 / 1024^3 = 59.6046 GB.
This discrepancy is also apparent with the stock iPod hard drive, any memory card or USB flash drive, and the hard drive in your computer.
So in short, the reported capacity of 60 GB is normal.