I'm calling it right now.The evidence:

This announcement only involves Sony:
It's on the NA and EU PS3 official blogs, there's going to be a Home premier of a trailer. There's not a whisper on the 360 side of things, i.e. no "FF13 Trailer on Xbox Live" or anything mentioned at all by MS.

This is supposedly "BIG":
I think the verbatim quote went, "by big I mean 'BIG.'" This practically gaurantees it wont just be an exclusive demo, I think the fanbase would riot if they're promised BIG news and it's a 20 minute sample of the game. What does this mean? Release date. And a lot sooner than you might think, as has been heavily hinted at recently. And that brings us to...

The actual release date: December 2009.
It's extremely obvious SE stands to make more money by having FF XIII available in time to ride the holiday wave. If at this point localization is ready, and we already know the PS3 code is ready for a Dec release, why not? How many more copies would FF13 sell if the release went PS3 ver in Dec, 360 ver in March, versus both versions in March? With the recent surge the PS3 is mounting, and how it's positioned to have a great holiday season, a world wide FF 13 PS3 bundle for Christmas just makes sense.

I say SE decided to void the portion of the contract that promised simultaneous release, return a portion of MS's money, and in the process reap the rewards of holiday sales.

its certainly plausable

nah

you want my point :

I will not believe it until it is Saturday and that hte news has taken the world by storm

what is sure is that it is not FFXIII going 360 exclusive

Still, rumor probability : highly improbable

Never gonna happen

If you say "360 timed exclusive in the west " now that could happen

it'll probably be something ultimately lame like announcement of trophy/acheivement list or w/e

I admit my prediction is bold, but 360 timed exclusive in the west is impossible. SE already took enough of a rep hit with Sony fanboys by bringing the game to 360 in the first place, and considering that's their target audience they wouldn't dare.

Plus, thats essneitally admitting to they took MS money and ran with it, and negate the "Oh we just want to reach more games" bullshit they've been doing damage control with.

i say its exclusive movable breasts of the Female characters via Sixaxis! :D

lol but i'd guess you're closer to the truth.  way to often this gen we've been promised big announcements only to get nothing special.

This could not be any more wrong. I'm sorry but that wouldn't be a "big announcement". It would get some threads going in VGChartz.