1.) Multi-platform Sales
Never before has a Final Fantasy game appeared on more than one console at release. Final Fantasy XI got ported to Xbox eventually, and a few of the games had PC versions, but FFXIII is the first newly released game in the series to hit two systems at once.
The move is great for players. Whether you own an Xbox 360 or a PS3, you can pick up Final Fantasy 13. There are some minor differences - the PS3 version comes on one disc, for example - but the game experience is exactly the same. Xbox 360 owners and PS3 owners can play the same game, and share their excitement with one another.
Other franchises are opening up a bit too. If you want to play Metal Gear Solid 4, you still need a PS3, but Metal Gear Solid Rising is hitting the 360.
When games go multi-platform, gamers get to choose the system they want, rather than get stuck with what the developer chose. If you prefer the Xbox 360 and it's ergonomic controller that you can actually change the battery in, get the 360. If you prefer the PS3 for its Blu-ray capabilities and free online play, get the PS3. Final Fantasy XIII is on both systems, so there's no need to worry.
It's an amazing setup for Squaresoft too. Rather than bet all their money on one system, they're able to maximize their profits by selling the game to a much wider group of players. More money for Squaresoft means better funded games, or more of them. Either way, the consumer wins out again.
This move also opens up the series to those who haven't played a Final Fantasy game in the past. Some people only own the Xbox 360 for shooters and never gave RPGs much thought. Putting the biggest RPG franchise ever on their system is bound to turn some of them into JRPG fans.
The characters, the story, the battle system and the streamlined nature can't compare to the importance of this game going multi-platform. Exclusives will never die, but for now, it looks like Squaresoft won't be making them.