I could believe a release 6-12 months after the PS3 release, though I still wouldn't hold my breath.

This rumor has popped up a lot of times, but there have been quite a few times where this rumor comes from a credible source who says it comes from their own credible source. That of course doesn't make the rumor true, just makes it interesting.

Four reasons I can think of:

1) After 10 years of dominance, Sony detractors smell blood in the water and can't help going nuts. Some may even believe keeping the rumor alive will hurt Ps3 sales, and become a self-fulfilling prophecy (ala RE4).
2) GTA4, DMC4, Assassin's Creed, and many other titles set a precedent, as have past MGS titles.
3) Sony reps have a way of saying things (UT3 is exclusive) that aren't always wholly true, so everyone but the most devoted fanboy tends to overanalyze every announcement for "hidden truths."
4) Maybe, just maybe, it's true(in which case the question would be why do people refuse to accept it).
One way or another we'll know the truth in 2008.

Didn't you know, according to fanboys, UT3 will never come to 360...because Sony said its exclusive.

The main reason it isn't going away is because people keep citing their "credible" (The last time we heard that, the source was a Swedish gaming forum, =) sources and posting in every gaming forum on the net.

Even if the rumor sounds plausible, or if it even does become true, at least wait for Kojima/Konami themselves to come out and say it. Everything else is pure speculation, nothing more to it.

 Sony said it was exclusive this year. What conferance were you watching?

I still expect a 6 month to a year delayed release onto the 360. I don't know why it's the end of the world for PS3 fans if it's ported. If anything you should be happy that more people will get to enjoy this unique gaming experience. I never understood people who care more about their console's success than the games they play on it.

It'll come, it just won't be capable of enjoying PC-created mods and levels as the PS3 version.

Sorry, I didn't know Sony said it was exclusive for this year.

Still, that's not my point...when Sony says Haze or MGS4 is exclusive, the fanboys seem to think that can never change...

 Too true.  I'll get UE3, but for the PC.  Buying it for a console is silly just like buying Oblivion for the console is silly.  You get the best for those games from user created content.  I know they said the PS3 is going to allow user created on it, but I still won't be able to make my own content on it and that's what I'm really interested in (and I'm not going to own two versions).

Right, but for obvious reasons "this year" wasn't exactly emphasized or repeated. It's more one of those clauses that you hope no one will notice (and many did not), and if people interpret it wrong, well, why bother correcting them?