Well, like any product, they rely on suppliers, which rely on raw materials. And sometimes product designs take longer to finalize than a company would ideally hope for.
Still, Sony arguably dropped the ball, with this generation of console coming out a good 6 months after Microsoft’s XBox360, and not having the availability (nor more attractive entry price point) of Nintendo’s Wiiiiiiiiiiiiiiiiiiiiii (Extra i’s added by me). It will be interesting to see if this hurts Sony’s current dominance of the videogame consol market.