So now that we agree that a game would be different from one console to another (you say 10%, I say depending on the effect, a lot more, but lets go with 10%), lets talk a why they do it.

Two main reasons. Money and desire. 

Money. You say it's bad for developers, but let's say a developer is going to release a FPS like Half Life, and they predict on the PS3 it will sell 1.5 million lifetime, and let's say that makes them 15 million in profit, after it's all said and done. If MS comes along and offers them 20 million to make it exclusive, they make more money. The only downside for developers is the loss of knowledge. Every time you develop a game for a platform, you learn more about that platform. Other then that, it can be a good thing for developers.

Desire. If your a good enough developer to be making todays best games, you are making a lot less money in the gaming industry then you can make somewhere else (and I mean a LOT less money). So if that's the case, why are the worlds best programers making games? The are passionate about it. They want to make the best game ever. I am sure of the creator of MGS4 had told his development team that they were going to make MGS4 at the level where it can run on the Wii, half his team would have left. They don't want to make something that has been done before. They want to create a game that looks better then anything the world has ever seen. That's the reason they make games in the first place. Now not everyone is like this, but that's why 90% of all games are multi-plat.

What makes you say that ?

 I was at the Sony presentations at GDC 07, ive seen this stuff before(the game those assets were for has been cancelled BTW) and fact remains that whatever you see onscreen still has to go trough the graphics processor so the constraints of the graphics card remain.

It can help with some pre calculation of secondary routines and stuff yes but CELL is not a magical processor, it is a simple PPC core(same one as we find in the XBox 360 with the difference that the 360 has 3 cores) aided by dsp like processing units.

The SPU`s add up and substract real fast and that is all they are good for so you have to synchronise their data and program them individually.

 Your posting history which includes admitting to trolling. The fact that you named a game that sold well over a million copies means you are just throwing out games you know the name of hoping to get a reaction.

Urm no, I have this from talking with the actual developers.

In the industry it is widely known that third party games underperform on Wii, so much so that people are publicaly calling for Boom Blox to be released on Live and PSN.

Exclusivers are better they bring out what's best in a system like Metal Gear Solid 4.

in most cases the exclusive titles are the ones that stand out the most anyways, for all the reasons listed above. there are of course exceptions in the multiplat games, but the truly refined titles like MGS4, GT5, R&C, uhh... whatever title they have on the 360, i guess gears and halo, i would have listed bioshock but that's now confirmed to the PS3(if anyone can point out a reference title for the 360, go ahead)

being able to focus solely on one platform, it's hardware and resources being exploited as well as possible, allows for the best games, IMNSHO :p

though yes, if the game PUBLISHER, is simply a money grubbing whore, Ubisoft and EA come to mind for some reason, then Multiplatform is the way, RA RA RA!!!!

Western developers in general made multiplatform games while up till this gen, Japanese developers made generally exculsive games

I think you mean all it does is math real fast. 

I agree with you. That's all it does. That being said... all a CPU ever does, is math.

I am all for multi-platform games, at least if no design or technical sacrifices will be made. Like with regard to Ghostbusters, the devs stating that the game would be better if it would have been PS3 exclusive, they could have had twice the action on screen as compared to the current PS3/360 version.

Or games like GTA IV have seen sacrifices to still fit on the 360's 6.8 GB dual layer DVDs. Multi-platform devs during this generation of HD consoles will usually have to ship with fewer game assets (like graphics/audio diversity) or they need to sacrifices on graphics/audio quality. The same goes with regard to tapping the potential of a default harddrive (which can help a lot with regard to streaming/caching) or non-shared RAM (more bandwidth).

Other issues, making games which make good use of Sixaxis motion controls or focuss on Playstation home integration.

The Final Fantasy XIII devs once stated the PS3 is the best console for them to suit their imagination/creativity. The devs asked beforehand if they could design the game as a PS3 exclusive as the game engine / assets would then be designed differently. Luckily the answer was "of course", as a result the games developers can be more ambitious with the game.