I don't think you understand. The four months you're talking about mean very little in total WW sales for the year, but the extra 8 months after Europe's launch certainly do.
Here's a look at PS2's 2000:
http://vgchartz.com/hwcomps.php?cons1=PS2®1=Japan&cons2=PS2®2=America&cons3=PS2®3=Total+Other&start=36583&end=36891&weekly=1
Japan - 44 weeks, 3,549,355
America - 10 weeks, 1,322,589
Other - 6 weeks, 759,973
And here's PS3's 2007(with 2006 included):
http://vgchartz.com/hwcomps.php?cons1=PS3®1=Japan&cons2=PS3®2=America&cons3=PS3®3=Total+Other&start=39026&end=39446&weekly=1
Japan - 60 weeks, 1,691,217
America - 59 weeks, 3,524,398
Other - 59 weeks(41 counting after Europe launch), 3,649,393
At the PS2's point in time, PS3 was:
Japan - 44 weeks, 1,177,725
America - 10 weeks, 919,885
Other - 6 weeks counting after Europe launch, 907,415
So with the extra time PS3 gained:
Japan - 16 weeks, 513,492
America - 49 weeks, 2,604,513
Other - 53 weeks(35 counting after the Europe launch), 2,741,978
For a total of 5,859,983. That's 228,066 more units than PS2 sold in 2000 alone. You may not like breaking the analysis down to regions, but clearly all the extra time included as PS3's first year makes the comparison flawed.