I would just say that "we won't compromise on quality" is their fancy way of saying "we miscalculated, and it just won't be ready on time" and believe them. But, I dunno, I still smell slight bullshit. They're asking for an extra three months or so, and you'd think if they needed that much longer, they'd have noticed before it was time to ship (which would have been within the next couple of weeks)
I dunno, I've heard a few theories, like that they wanted to release their game at a time when everyone's wallets hadn't been recently crippled by the new console releases, but I still think they stand to loose more than they gain, especially as they're now aiming for a pretty dead time of year. They'd have the market to themselves, but to forfeit the holiday season? Surely not. Then again, it's one hell of a holidays season, again, given the new consoles. So who knows.
In the end it's up to them to choose when to release anyway.