I'm pretty sure every time someone tries to say this, it gets countered with actual data showing that XIII sold quite well.
edit: here you go
VII = 9.8 mil
VIII = 8.1 mil
IX = 5.3 mil
X = 6.6 mil
XII = 5.2 mil
XIII = 6.9 mil
http://en.wikipedia.org/wiki/List_of...ng_video_games