You mentioned looking at PS2/PS3 hardware from launch - this can't be done worldwide (no Others data for PS2, apparently), but it can be done in America and Japan:
http://vgchartz.com/hwlaunch.php?cons1=PS2®1=Japan&cons2=PS3®2=Japan&cons3=®3=------&weeks=156
http://vgchartz.com/hwlaunch.php?cons1=PS2®1=America&cons2=PS3®2=America&cons3=®3=------&weeks=156
PS3 is under half of the PS2 in both regions.
Edit Bonus: Make that third line Wii or GameCube and you might notice something interesting.







