DVD is increasingly showing a strain in providing HD content.

[MikeB]

@ WilliamWatts

Developers have often complained about this, but they usually don't want to damage the reputation of their product in public by highlighting how much better their game could have been if they would only have to take into account Blu-Ray.

Final Fantasy XIII for example, comes on three 6.8 GBs 360 DVDs with downgraded ingame textures and cinematics on the XBox 360. They also stated they cut so much out of the game they could release a new game based on that alone. I think it's not unlikely that if the 360 would also have enough capacity more of this content would have made into Final Fantasy XIII.

It could have been a consideration as that would mean even more discs on the 360 or more downgraded assets quality. Square Enix prefers to claim both versions are on par, because bad PR and upset people does not help their bottom-line.