Both of the HD consoles launched at a higher price than any succesful console ever had, so it seems to me they included lower end SKUs to provide an alternative for people on a budget. Also the internet plays a larger role this gen, so now fanboys can use the lower price and higher specs when arguing which console is the best. =P
I'm not sure why Sony did the 80GB bundle, but I'm guessing they're trying to increase revenues by adding more stuff rather than dropping price. Adding 20GB, an extra controller and a first party game probably costs them less than $100 per unit, and they're hoping the customers will be wanting to get that stuff anyway, and treat the new bundle as if it was a hundred bucks cheaper than the identically priced 60GB one.







