Basicly playstation in order to cut costs made version with a smaller(40gig) hard drive and without the software needed to play the playstation 2 games.
Then they discontiuned the mid range 60 gig version i belive and dropped the prices on the 80 gig version.
Basicly they are no differences in the 60 and 80 gig versions besides the hard drives.
Sony has been beind the Xbox 360 and Wii in console sales so they decided to make a lower cost version to ramp up sales.