With Square Enix having completed the Story and Scenario modes, they're fixing up the other areas which need attention. The graphics are 80% complete while the battle system still needs "refining and perfecting."
When asked about DLC for Final Fantasy XIII, Square Enix said that there aren't any plans in place to support it. Which is both a good and bad thing - good because it means wallets won't be milked Namco Bandai style, bad because it means there won't be any post-release support to inject new life into the game.
Still, with Final Fantasy XIII due for release in Japan at the end of this year, there's a lot of time for that stance to change. We shall have to wait and see.