In my experience, shipping a product as polished as Mac OS X 10.6.8 Snow Leopard requires a painful level of dedication from everyone involved, not just Quality Assurance.
As long as neither the New York Times nor the Wall Street Journal writes about how bad Apple’s software has gotten, there’s even no reason for them to think about changing their approach.
The drama surrounding Apple’s software quality isn’t showing up in their earnings. And at the end of the day, those earnings are the "high order bit," no matter what marketing tries to tell us.
How?
How do you reproduce something when you have no idea of the cause and it's not happening on any of your machines?
And remember they don't have just this one unreproducible bug reported. They have thousands.
If you have experience writing software, you're going to end up with a lot of unreproducible bug reports. They're a genuine challenge for everyone, not just Apple.