You also have to factor in price cuts for the other systems too. Something I think a lot of people are ignoring. Plus at some point the PS3 should be profitable, which it won't be very much if they cut the price every year or 18 months.
Anyone can guess. It takes no effort to throw out lots of predictions and have some of them be correct. You are not and wiser or better for having your guesses be right. Even a blind man can hit the bullseye.