Sony's 13,000 song measurement is based on its ATRAC3 (Adaptive Transform Acoustic Coding for MiniDisc 3) compression system at the relatively low rate of 48Kbps (kilobits per second) while Apple's measurement is based on the AAC compression system at 128Kbps. At the same bit rate, the Walkman can store around half as many songs as the iPod, which is consistent with it having half the storage capacity.
Source: MacCentral
Nice to see Apple making this statement since AtAT did the same thing a week ago. Now the figures might get more attention though. Silly Sony, what in the world were they thinking?
