why FF13 sucks on 360
I believe it's all related to the type of HDR being used in FF13, namely the Logluv. Logluv is a type of HDR first used in Heavenly Sword (it's also being referred as NAO32 in honor of its creator Marco Salvi the nAo), and it's been used in various games such as Uncharted 2. I suspect Logluv is being used in FF13 from the dithering artifact seen on character's hair. Logluv doesn't support alpha channel for transparencies (which only includes the ones that are affected by lighting, particle effects like fire, smoke etc don't count) 360 on the other hand, has got its own unique hardware enabled HDR format called FP10. FP10 provides 2 bit alpha for transparencies, however we see the same dithering artifact on the 360 version of FF13, which leads me to believe that the 360 is also using Logluv . And that's where the problem starts because with Logluv, you are not able to take advantage of EDRAM.
http://psinsider.e-mpire.com/index.php?categoryid=3&m_articles_articleid=599
(Check out Marco Salvi's interview for more info on Logluv/NAO32)
So, what had been the major advantage 360 had over PS3, becomes nothing more than a liability now.
This is so interesting, because I see Logluv as the major player in giving PS3 the upper hand in visual department over 360 on its exclusive titles.