If Pharmasset had kept the drug for themselves, they would have launched at a similar price.

Early on in a drug's development, companies will do market research to estimate the value of the drug. That research is pretty quick and dirty and the price you arrive at has a margin of error of +/- 50% easily.

I have acquaintances who worked on the pricing of Gilead's drug. If anything, Gilead priced at the lower end of what they could have. No company, launching that drug today, would have priced it at the price Pharmasset estimated 2-3 years ago.