I estimate at the very MINIMUM 2 million. If you go to most gaming sites you'll see hundreds of forums of 360 owners that are converting to the PS3. I think the PS3 is slowly but surely making its way to number one (if it already isn't) in the next gen race.
Your question is: How many people are going to spend $460.00 + Tax for one game?
Answer: A few. But it's not going to be significant enough to drive a nail in the head of consumers. Most people are not going to go and buy 2-3 systems, let alone for one game.
John your mistaken by how many people are impressed with the PS3 now, the 360 only brought better graphics not much else unlike the PS3 who brought a number of NEW things to the table