I know you all like to think when the price comes down to PS2 levels it will start selling PS2 sales levels, but that is a rather silly assumption. Sales are not wholly dependant on price.
If the PS3 has it's next price drop in early 2010 (it will likely be later than that) say a further $100 off, it will help sales for a while before it dies down again.... being at a similar price to the PS2 would have done wonders for the PS3 if it was at, or near launch, but that late into the cycle it is more a move to keep sales at a good level for a bit longer rather than dramatically increase sales.
True, the huge launch price may help Sony to keep the PS3 alive a bit longer, because they have more room to drop price (ie lose $100 each year) but Sony are not going to be able to bring the price down fast enough before people are getting into the next generation properly, even though Nintendo and MS are probaly willing to stretch this gen, it will be at least 2 if not 3 years from now before the PS3 could be at the current Wii price, which is still a high price for a console, but more dramatically so when said console is 5 years old.
Even so, 50 million is well within reason, and with some luck, 75 million is a possibility (right out on the edges of possibility) but the most likely scenario (ie I would say an 70% chance of being in this range) is 45-50 million.