I bet this comes down to:

A) Projected amount of PS3's in circulation
*
B) Projected Attachment Rate
*
C) Revenue from MGS4
=
...well if it isn't multi-million-enough to cover this game and make a profit it will be developed for the 360...

So it could already be under development for the 360 if their projections come up shallow.

(I hope my pseudo math is correct)

The rumors won't die because, as someone said before, it's plausible. This isn't like the FFVII remake rumors that have been flying around since 2001. Konami sank a lot of money into MGS4 for YEARS and more than a good deal of the current PS3 fanbase would have to buy it for them to see anything close to profit. At the moment, it's very unlikely.

Kojima has no say in the matter. He can whine about his "vision" but if MGS4 tanks, that's Konami's money going up in flames. MGS2 may not have done well on Xbox but as we've seen before, Konami has no qualms bitchslapping Kojima out of the way and porting Metal Gear around.

It is definitely plausible not only Konami can cash in with a larger audience but Kojima is no longer useful to Konami. MGS4 is the last game he is going to make(correct me if I am wrong) and why would Konami care about Kojima once MGS is done?

Kojima said it was the last Metal Gear game he is going to make, so presumably he will stick around for some time working on other stuff like a new Zone of Enders and some other new IP's.

In any case, I am sick of these rumors. If it comes to the 360 eventually, then so be it, but these "inside source" things are getting really old. The fact that this one comes from an Xbox oriented magazine (a bad one at that) only makes me disbelieve it more.

No, it's not his last game, it's just his last Metal Gear game. He has strongly stated that his next project will be a Wii game. Keep in mind that this hasn't materialized into actual projects, so until it does, it's just speculation. Still, his wording is very strong:

http://kotaku.com/gaming/kojima/kojima-doesnt-care-about-hd-interested-in-wii-225925.php
http://www.computerandvideogames.com/article.php?id=140020&site=psw

Key quotations:

I've played Tennis, Zelda and Mario on Wii. I find Tennis very interesting. I played the early version but the E3 version is far more advanced. As a game designer, I'm very interested in creating something for the Wii. I'd like to run away from MGS 4 creation and create something for the Wii but unfortunately, I don't have anything that I can announce at the moment. I have lots of ideas for Wii but I have a heavy schedule with MGS 4 and Metal Gear Online.

Wii! [laughs] Yes, I want to do it. I'm saying this everyday. But first, I have to face this giant that is called Metal Gear Solid 4, so until I'm finished with that, I can't do anything... We're not the ones who are saying we want HD. I'm not interested, myself, about HD at all. MG games tend not to care about how clean the screen looks...we deliberately make the graphics look dirtier to give the atmosphere more life.

The rumours persist, because everyone knows the game won't be profitable on the PS3 alone, or at least it would make more money as a multi-plat. Even last gen we saw remakes of all but the latest part end up on other platforms, and that was when the Playstation was doing ridiculously good. This time the Playstation is selling the weakest, but some people still expect it to stay exclusive?

The only question is wether they'll port the main game itself within a few months of original release, or wait a year or so to do the remake.

I wouldn't expect to see much stay exclusive to the PS3 this generation, unfortunately, I don't see much exclusivity for any console. This generation will probably warrant the title of "The Whore Third Party Era".

No... Atleast I didn't! Did they go down or what?! And if so! How hard?!

You see this as a bad thing? I think it's great we won't have to buy more than one console to get to play a good chunk of this gen's best games. Well maybe two, since it looks like the two biggest groups are going to be 360/PS3 multi-plats and Wii exclusives. 

Makes more sense to believe in Sony than trollposter#256, dont it DUDE?