Still don't understand how this is as big a thing as you're making it out to be.  It's good for MS, it's an advantage.  But it's not coming to Japan, and PS3 owners are still getting it.  It's big for a potential 360 owner or potential PS3 owner but for current owners it doesn't matter.  And in the grand scope of sales, PS3 sales will be > than 360 sales.

Lets do it region by region:

-Japan:  Due to being the second console in a one-console country, there is a serious cap on the capability of any game to boost the PS3 in this region.  This was demonstrated most recently by MGS4.  In any case, multiplatform status in this region would have had no effect based on past game/console sales for the Xbox 360.  The region is already smaller than the West for FF sales and is shrinking rapidly.

-West:  Here the majority of FF sales are made, and Microsoft rules the roost with over 50% more consoles.  Most importantly, the SKU that can easily handle single-player RPG's is HALF the price of a PS3 in Europe, and MUCH cheaper in the USA.  Already on this forum alone over a dozen people have said they will no longer need a PS3, and others have said they will sell their current one.

When all is said and done, there has just been a substantial shift in momentum from Sony to Microsoft, the full extent of which will be prolonged and immeasurable, but nonetheless substantial.

You're almost as bad as Sony by grouping together "The West" rather than by region.  Japan will have the largest software sales, and will push consoles.  Others will have the smallest software sales, where the PS3 will win by a margin.  America is pretty sketchy, but depending on where the sytems are when the game launches in america (could be 2 years + from now), I'll reserve judgement until then, but with recently the PS3 besting the 360 in America, it could be 50/50.

You continually want to push this whole "pushing consoles" concept, instead of actual sales.  FFXIII isn't going to push consoles outside of Japan.  First of all, people who want JRPGs would have already went 360 for Star Ocean, IU, Last Remnant exclusivity, etc.  Final Fantasy XIII isn't going to be some major push in consoles. 

As I've stated.  This is a win for 360.  Not as big as you're making it out to be, but a win, nonetheless.

What are you comparing this too?  The comparison making is between what we could reasonably have expected if the game stayed exclusive and what we can reasonably expect now.  From a sales perspective, all that matters now is if/where/ and for who this game pushes consoles.

To suggest that it wont is ridiculous.  Take a glance around these forums.  People are ALREADY saying their PS3's are going up for sale.  Other's are saying their mind has been made up on their HD console of choice.  PSrock has gone into meltdown mode and lost all hope of emotional survival (never a good sign).

The very fact that every internet forum still working has dozens of posters each declaring the PS3 wont catch the Xbox 360 this generation signals a shift in momentum, whether it is true or not.  I don't care about sales of the game itself.  They will be 65/35 total to the PS3, but the game will have sold a LOT more for having been multiplatform in the West.  Whats important is that the West, parts of which love the Xbox 360 and the rest of which don't mind it, now have a far cheaper option (and one that is FAR more appealing for JRPG fans) for picking up FFXIII.  An option they will adopt in droves.

The last FF sold slightly more in the West than in Japan. This was from a total of just over 5 million units.

FFX sold around 8 million units, with a substantial advantage to the West. The Xbox 360 has a lead of around 7.5 million consoles over the PS3 in the West, a lead that is likely to remain, or alter slightly depending on price drop occurences for the Xbox 360 and the PS3 in North America.

There are a large number of people in the West and in Japan that will buy a console specifically for FFXIII. In the West, due to the large number of exclusive, reasonably high quality JRPG's avaliable, the Xbox 360 is likely to perform well in hardware and software related sales of FFXIII.

In Japan, the only possible boost will be to the PS3 due to the game's regional exclusivity, but over the last hour a couple of fundamental mistakes have been made alongside some of the assumptions regarding what FFXIII can do for the PS3 in Japan. The PS3 will not see a PS1 or PS2-like FF-related boost in Japan. Not only is Japan's relative importance to FF sales declining, but the Japanese hardcore market is declinging (quite rapidly according to last months Media Create aggregates).

But more than anything, for the first time in three generations, the Playstation console is not Japan's console of choice. MGS4 has shown us quite clearly that there is a very definite, and abrupt, limit on how far good exclusives can push a runner up console in Japan.

It is probable that the worldwide hardware boost caused by FFXIII will be larger for the PS3 simply because the console has a Japanese exclusive. However, what might have been a major worldwide boost over the Xbox 360 will now be mitigated almost to the point of irrelevance. The Xbox 360 could have had a day and date arrival of FFXIII in Japan, and just like DMC4 and other multiplatform titles, it would have done nothing for the console in that region.

Today saw a MASSIVE blow to Sony.

I agree with basically everything you said.

However, I would really like to know what the exact reason for not releasing an Xbox 360 version in Japan might be. Consider this:
- the game is developed in Japanese language
- the game is ported to the Xbox 360 anyway
- how much additional work would a Japanese 360 version require? (close to nothing imho)
So EVEN if doesn't sell well in Japan, the gains would definitely outweigh the (supposedly very low) expenses. So at the moment I don't understand why they don't release it in Japan.

Okay Starcraft.  Sure.

I'll wait and see when the PS3 sales stop.  I'm most assured that this one game going multi-plat would have single-handedly killed the PS3.  And we're talking about a game that isn't coming out in the U.S. for at least 18 months, and as much as 30 months, with an EU release date to follow.  By the time FFXIII launches, we'll definitely be in the phase for the next XBOX 360 at least.