Except the vast majority of PS2 gamers who never played a GT game...

there is anyone in the world who haven't?

And the vast number that never played GT1/2 on the PS1 but bought GT3.

I suspect the question is more in regards as to how this community would react. Every time Sony loses another exclusive title the PS3 fanatics go through certain stages of mourning. The stages of mourning are as follows outrage, frustration, attack, denial, ignore, and fester.

First they are outraged mostly due to the fact that for them any exclusive game becomes an article of faith. Second they give into frustration at Sony for once again not doing what they should have done to keep the title exclusive. Third they attack the developer for being a duplicitous bastard. Fourth they deny that they ever had any high expectations of the title. They even deny having a high opinion of the developer. Fifth they do their utmost to ignore the title entirely going so far as to call out other members of the community for even mentioning the game. Sixth they go right to the rot, and suffer in silence. Letting what happened slowly eat at them until it makes them mean and antisocial.

For the rest of the community it is more like kicking somebody while they are down. The defenses are already known, and are easily bypassed. After all there is something gleeful about attacking a zealot when their faith is at low ebb. The arrogant veneer once shattered is like blood in the water. Beyond that they really did not care, because whether a game comes to their platform or not is irrelevant to them. For those that own a 360 of a Wii the reality is pretty simple their highly anticipated exclusives really do not defect.

Would it effect the console war in a real fashion. Well yeah but the effect is negligible. The real consequence is one of attrition. The effect is only appreciated in conjunction with all of the other exclusives that Sony will have piddled away. Every time Sony loses an exclusive it undercuts morale on the part of owners, and tarnished the reputation of the brand. So these losses do eventually take their toll on the console. Hardcore players pass on their experience into the more core audience.

Every time a hardcore player tells their more casual friend they can get that game on the 360 as well. That causes their friend to ask the question why spend more money then I have to. Which is basically very logical if your just a fan of the series why spend two hundred dollars more to play. Pick up the game and the cheaper console.

what would happen?

The earth would explode, up = chair, and the 360 will cease to RRoD

If only they knew the reason-- "Compares PS3 dev kit to 360 dev kit.  Hmmm.... Which one?"

Like with FFXIII and MGS4! The apocalypse approacheth o_0

 All fixed, but MGS4 has yet to make its arrival.

Oh, then the apocalypse isn't here yet. Right now its only about the way of the crazy guy with the sign has been yelling it for a while(MGS4 rumors) and nobody cared because he was a nut. Then signs started appearing in fields and such with apocalyptic messages(Konami PR rep speaking) and now people are starting to get nervous. Still, its uncertain and may well never happen, but things are looking pretty crazy.

The same thing that happened when FF13 became multiplatform:

avatars/sigs would be changed
the developer, slandered
the game, attacked
and a new exclusive title would be picked as the holy grail of the platform