http://vgchartz.com/hwlaunch.php?cons1=PS2®1=Japan&cons2=PS2®2=Japan&cons3=PS3®3=Japan&weeks=104
http://vgchartz.com/hwlaunch.php?cons1=PS2®1=America&cons2=PS2®2=America&cons3=PS3®3=America&weeks=104
http://vgchartz.com/hwlaunch.php?cons1=PS2®1=Total+Other&cons2=PS2®2=Total+Other&cons3=PS3®3=Total+Other&weeks=104
As you can see, the PS3 is performing dramatically worse in Japan, dramatically worse in North America, and is tracking somewhat similarly in Europe (although it is difficult to tell being that that the chart is broken, early on the PS2 faced bad shortages in Europe, and the PS3/PS2 have different offsets in the year for when the systems launched). On top of that we know that even systems that "last" 10 years see the vast majority (75% to 90%) of their hardware sales in the first 5 to 6 years on the market; and the lifespan of a console is heavily determined by how well it sells in the first couple of years on the market.
With all that said, I expect the PS3 will sell at most to 40% of the PS2's levels in Japan and North America and overall will achieve 40% to 45% of the PS2's sales worldwide ...
