As game engines and other technologies improve, this may change. However, before that time, most games will come out on DVD. Blu-Ray wont be the standard until later.
In Sony's on conference, their rep said for the first year only 20% of the games that came out for the PS2 were on DVD. Then 5 years later that number was up in the mid 90%. Granted that's impressive, however, it appears that the next-gen cycle is now shorter than 5 years. The xbox was not out for 5 years, and I anticipate that the companies will be launching into their next-next-gen console pre-production around 4 years from now, with a release one more year after that.
That being said, if Blu-Ray is not the de facto standard for next-gen data storage by this point, Sony will lose a large chunk of change, even at $499 and $599.