20GB PS3 Still Goes For More Than 60GB PS3

1.
Sony PlayStation 3 (60GB)
by Sony Computer Entertainment
(Nov 17, 2006)

(PlayStation 3)Buy new: $599.99   
43 Used & new
from $599.99

2. 
Sony PlayStation 3 (20GB)
(Nov 17, 2006)
(PlayStation 3)

9 Used & new
from $719.99

-- Amazon.com: "PlayStation 3"

Some economics student could write a thesis on that. I mean - WTF? The PS3 is regarded as expensive enough at the retail MSRP for the 60GB version. So why pay a $120 more to get the lower end model off auction?