Rumors come, and then they're smashed. That's just how this industry goes. Sometimes they actually turn out to be true, but I'd venture to say that a vast majority of them turn out otherwise. Such is the case of Final Fantasy XIII's 2008 release date.
This one actually came from the mouth of a Square Enix employee, so it seemed to have a bit of credit behind it. Unfortunately, it sounded too good to be true, and was later proven to be so. Square Enix made an official statement saying that they have made no official statement, and anything we've heard so far is nothing more than hearsay.
I'd say that it may still be safe to hope for a playable demo sometime this year, but I wouldn't hold my breath. Sure, I'm a bit bummed to hear this, but I can't say that I'm too surprised. Besides, the year's barely begun, there are plenty of other good games to look forward to.
[via Square Enix]