SCE made those projections based upon information they knew ahead of time before the general public did.
If the 13m projections had been for a $399 PS3, then yes, everyone would be absolutely right to think SCE's projections were unreasonable at the very least, peyote induced crazy fantasy at worst. But those projections were obviously made around a $299 hardware revision in time for the holiday season.
This is why many people who predicted a $299 slim knew it was coming when SCE released its annual projections. It was the only feasible way they could hit 13m.
As for these projections being low, everyone who believes this post a list of consoles that sold 13m in a year at $399 for the first half of the year, and $299 for the back half.
1. ...
2. ...
3. ...
My guess is there will be exactly one console on that list in about a month.
Secondly, for those who deliriously believe 13m/year is where the PS3 is going to peak, it must be based upon insider information that the PS3 will in fact be stopping production at $299, either because SCE plans to sell the console at that price for the next 7 years, or because SCE plans to exit the console business before they drop production costs/MSRP again.
The majority of total sales for any given console has been under $199 without fail since the inception of the console business. Does anyone actually think the 7th gen will be any different?