The PS1 doesn't have any data for Europe or Americas here.... so that graph is purely Japan.
And to get around the spaced out launches, why not try and do them regionally?
PS3 WAS tracking with PS1 in Japan, but the PS1 had a slow start, PS3 doesn't look like it will pick up.
http://vgchartz.com/hwlaunch.php?cons1=PS2®1=Japan&cons2=PS3®2=Japan&cons3=PS®3=Japan&weeks=156
In America there is no PS1 comparison, but PS3 is well behind PS2
http://vgchartz.com/hwlaunch.php?cons1=PS2®1=America&cons2=PS3®2=America&cons3=PS®3=America&weeks=156
In Europe (not including"others") PS3 is doing well, it will fall further behind PS2, but for now it is keeping with it although 1 million lower.
http://vgchartz.com/hwlaunch.php?cons1=PS2®1=Europe&cons2=PS3®2=Europe&cons3=PS®3=Europe&weeks=156
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So if you want a WW comparison you have to take some months off PS3 in Europe/America.
