Here are a few reasons:

Source Code :If you go to the site and look at the source code of the site,it has words METAL,GEAR,etc in it.I don't think Kojima would be such a fool to write the words of the game in the website's code when he is trying to make us go round and round.He could have just put it there to make us think it is a Metal Gear Solid game when it is not.That way we would be buzzing about it and wudn't pay any attention to find out what the orignal game is.

The Countdown Timer :He is putting all these timers out and making us wait so long to get excited about his next game.And as found out by the website,the countdown timer ends on the day of MS E3 conference.That way he is making us believe that MGS is coming to the 360 and adding more fire to it.But he is just playing with us.It could also be that when the timer ends on the day of the MS confenrence,he may put a timer for another 2 days which leads to the Sony E3 confenrence and fool us all.

The Images and Numbers : The website is being constantly updated with different images and weird numbers.That is another way he is making us believe is many different thngs

Conclusion : Don't believe the website that much.Whatever is there on the website proves nothing.The whole website can just be revamped at the time when the game is announced.It could be just to create add fire to the game.

The "The Countdown Timer" sound a little fanboyish to me.

I'm just going to say "wait and see."

No its MGS5 for sure.

why is it fanboyish?

its a countdown.

Just a few things. It's pretty much confirmed that KojiPro is working on a new Metal Gear game. Kojima's whole GDC speech was essentially about how could take Metal Gear to the next level and create the ultimate stealth game and quite frankly hinted at the end to the "Next Metal Gear". Then there's the Famitsu PlayStation issue coming in a few days that has a "next Metal Gear" in it. Finally taking another look at the mysterious letters in the sky, there's "5", what appears to be an "e", an "E", and a "3". I believe that joystiq has the best idea that the "e" actually represents a "@" in whatever funky font Kojima is using that is more than a little remeniscent of the promotional font for MGS4. If you combine those you get "5 @ E3".

Now I know Kojima is fond of playing with the minds of his fans. MGS2 was pretty much a huge mindgame for those that played MGS1 and the promotional videos and trailers for the game were intentionally misleading. Then there is arguably the whole i + ! = Power symbol promotion that many felt was an "obvious" sign of a 360 game in development because the letters were green. However, in my years of experience with Kojima he's never been so bluntly trolling as to actually call something and give a number of hints as to something that it was not. He never said we'd be playing as Snake all throughout MGS2. He never said that i + ! would be a console game.

Also, the countdown timer and the Microsoft conference are completely unrelated because it ends on May 31st, not June 1st. The source code dates are in Japan time. Microsoft's conference starts at 10:30am in Los Angeles. By then it's already June 2nd in Japan.

I don't think Kojima is the type to create false hype (not that I know alot about him).

Too bad Kojima got banned from the site (made some Xbox fanboys angry), we could have asked him,

directly oh well....................what? you don't believe me

ok check his profile below

http://vgchartz.com/profiles/profile.php?id=42828

*gasps*

Well, there is a new contender in town, it seems.

Is Kojima Working on Lords of Shadow?