I've read it and it doesn't make sense to me at all ( even if that indeed turns out to be the reason ) as once the game was to be released at the original date they could have hyped it up for the second time before Christmas I reckon unless there's something they fear will be an enormous letdown once it releases ( Standard cars perhaps? ) and spreads from word to mouth.
If so and their tactic seems to be a massive amount of sales during the holiday season peak worldwide and less on consistent sales during a long lifespan they wouldn't be very confident about this product now would they?
If not and they somehow fear to be crushed by a huge Microsoft Kinetic campaign diverting attention from their GT5 campaign shows they probably seriously underestimate how many people look forward to GT5 and will buy it the second it comes out regardless which company campaigns what, and even when they want to persuade the casual gamers who may not be aware GT5 is coming why wait after a huge campaign by your main rival which may persuade potential PS3 customers?
Again if GT5 indeed is the game worth waiting for ( ahem ), why not have a second campaign ( big and/or clever ) once the holidays arrive?
You would still gain new customers without pissing off the existing ones but then again what the hell would I know of marketing?