Sony America VP of marketing, Scott Steinberg, admits in an extensive interview with GameDaily that the company underestimated the demand for the 80GB PS3. He says the $100 extra for the 80GB model at $499 didn't seem "that big of a deal" to certain consumers. Beyond the price and obvious drive space difference, the 80GB enjoys backwards compatibility with many PS2 games, which the 40GB does not.
Steinberg states Sony is replenishing the marketplace with the 80GB model and expects to see "mass market appeal" from the upcoming $500 Metal Gear Solid bundle. At a minimum, expect one significant change in future PS3 models with the Sixaxis being tossed out and the DualShock 3 becoming the new hotness.