Wii HD launch title ;)
Square-Enix probably does not want to get stuck next fiscal year without a big game to make their spread sheets look good. If they use up both DQIX and FF13 this year, they likely are stuck up the creek without a paddle for next year.
Besides really it's not like they lose anything by holding off FF13. The PS3 + 360 userbase will only be bigger next year. I've never heard of a dev team complain about an extra 6 months of development time either.
I'm thinking April 2010 for FF13. This year S-E is set with DQIX, Kingdom Hearts 358/2 and maybe Final Fantasy Crystal Bearers.