According to a recent interview with Final Fantasy XIII's art director Isamu Kamikokuryou, the title was actually a much larger game before content was cut; so much so in fact, that the additional content could create another game entirely.

Lightning’s House with an exterior which is described as “park-like”
Levraut Store (?????) had an interior which was NORA’s secret base
In addition to Nautilus being an amusement park, there was also a Zoo
and more adding up to roughly ANOTHER FULL GAME

According to Kamikokuryou, the removed content was already running on PS3 hardware, but was left out when the team considered the game's overall balance and volume.

Now, if Xbox gave a 3 disc limit to it, they obviously removed things for a reason. They didn't say it was because of XBOX, but it should come as no surprise.

Before you claim "hearsay and lies," it would be strongly advised to research before you post your replies.

Because of volume, 3 disc limit... Click. It just makes sense guys.