i know it's really annoying, we would have only needed to wait another 10 days if it hadn't been pushed back. It was probably a production problem like eternal mentioned but others have suggested that the delay was a Marketing decision made by nintendo of america. This would make some sense for a couple of reasons. If Nintendo waits to print copies of the game they get to hold onto capital funds and don't have to pay for a while. They therefore make interest on the money that they continue to hold possession of. Now you may say that they'd make up their investment easily with the release of brawl. But keep in mind that NOA was somewhat dissapointed with the original pre-orders. If Brawl had been released and had taken a while to sell due to customer ignorance, then Nintendo would not make as much money and incur higher costs than if they waited a small amount of time to advertise the game. Considering that interest is compounded continuously, a month makes a very large difference on revenue.
This was a business decision, and don't get pissed at NOA since let's face it, they are a business. They seek to make the most money, and in a capitalist society, the best way to do that is to be the best, the cheapest, or the only. NOA is trying to accomplish all three at once.