Dude, the exclusivity of the game was confirmed at the conference by Kojima himself. I watched the conference, you can download the conference and check for yourself. Or read the article from IGN:
July 11, 2007 - During its E3 2007 conference, Sony confirmed to its fans exactly what they wanted to hear: Metal Gear Solid 4 is still exclusive to the PlayStation 3.
PS3 owners are no doubt shedding tears of joy.
Sony also confirmed the game would see a simultaneous worldwide release in early 2008. The game's designer Hideo Kojima will be demoing the game next week in Tokyo, and will be playing the game in front of an audience. Kojima said the game will "look a little crazy."
IGN: E3 2007: MGS4 Still PS3 Exclusive
The rumours will never die down though, seeing as how a new MGS4 to 360 rumour spread around every week.
P.S The trailer is in real-time, and Kojima's translater stuttered at the conference
