Poor graph choice as others have said.
This is from April through now, it shows up more clearly.
http://vgchartz.com/hwcomps.php?cons1=Wii®1=All&cons2=PS3®2=All&cons3=X360®3=All&start=39544&end=39740
The breakdown into regions that someone else posted is good too, but can't be compared with the PS3 as easily.