While this kind of marketing buy out isn't to my taste (and let's no remember Sony do it a fair bit in Europe, too) it makes sense for MS.
They clearly have two goals
1 - if you haven't already got an HD console and FFXIII is going to tip the scales they want to try and get as many such people as possible by having the only bundles for the game combined with marketing to focus the title on 360. This will be particularly important in US where MS is clearly going to fight Sony tooth and nail for every console sale and to preserve its lead.
2 - they want to raise awareness with 360 owners about the title to maximize sales and further expand 360 success with former Sony (and yes Nintendo, I remember) exclusives. MS know how most people associate the title with Playstation and they clearly feel (as with GTAIV) that they have to do all they can to get FFXIII aligned with 360.
It'll be interesting to see how this plays out in Western sales for FFXIII on 360 vs PS3.
There is a chance, which is the only interesting part of the article IMO, that this is all money being spent more or less for nothing - as I wonder how many people are really wandering around without either a 360 or a PS3 who'll plump for a 360 bundle, while I think most PS3/360 owners already know which platform they're going to get it on.
But MS has spent billions and is arguably still in the red in terms of total spend around Xbox so I doubt MS are too worried about that risk vs the possible upsides.
Try to be reasonable... its easier than you think...