I think the 360 version will probably have more compressed audio and video but that's about it. Also Blu Ray reads slower than DVD so duplicate files are used to combat this (as is mandatory installs).
This rumour about FF being purposely made worse so as to keep it parity between the systems is pure SDF type propaganda. Why on earth would they do that? Who has done that? There will always be small differences between the systems, they are different architectures and in multiplat face offs the 360 usually wins so if anything it should be the other way around.
About Bayonetta download file size disparity between PS3 and 360, well PS3 version is longer in some ways (to make up for the lack of the clock tower section).
What I want to know is how come the 360 allows one to download updates and games without having to install them? Does it install as it downloads? Why doesn't the PS3 do this? It's a right pain having to install after downloading.
