There are differing opinions on the sales of FFXIII-2, many people have written it off as a bomb while some are surprised its done anything at all considering the controversy its predecessor created; but with sales we have hard numbers in front of us and past milestones to compare to.
FFXIII-2's sales currently don't even match FFX-2's week 1 sales in Japan. Going forward the game will see massive drops in sales and I don't see it going much over 2 Million LTD; adding in Xbox 360 which shouldn't see past 500K we are seeing XIII-2 barely make more than X-2 made in Japan alone.
Now I personally feel the American sales are massively overtracked for PS3 anyway, so the sales are even lower in reality (NPD has proven VGchartz overtracked last month too).
The real "Final" Fantasy may not be that far away if the series continues on this course.