Every week :(
As many people have stated already the Playstation and PS2 data is incomplete although we can make other comparisons with data we have:
In Japan the PS3 is selling at (about) the rate of the Dreamcast and is below the sales of the Gamecube
http://www.vgchartz.com/hwcomps.php?cons1=DC®1=Japan&cons2=PS3®2=Japan&cons3=GC®3=Japan&align=1
In North America the PS3 is selling worse than the Gamecube and XBox did
http://www.vgchartz.com/hwcomps.php?cons1=XB®1=America&cons2=PS3®2=America&cons3=GC®3=America&align=1
And in the other regions the PS3 (after initial strong sales) is struggling to catch up being that it is selling at (roughly) the same rate as the XBox 360:
http://www.vgchartz.com/hwcomps.php?cons1=X360®1=Total+Other&cons2=PS3®2=Total+Other&cons3=Wii®3=Total+Other&align=1







