Making games on this level is hard work. You can't catch every bug, and there are things that are hard to test or plan for. A beta might have resolved some of that, but nobody can say for certain without knowing the innards of the project and XBL if it would have. I'm not going to pretend I know one way or the other but I do know it's hard work.
Additionally, I will say as a software developer (in a different field), that bugs absolutely are the bane of our existence. Especially in production. I've introduced bugs into my code, and when I don't catch it, the QA people don't catch it, but the customer does, I/we feel terrible. I can imagine that the guys at 343 that worked on this game feel the same damn way. You can call it ass kissing or whatever, but I know that it's not easy, and bugs are going to happen no matter how many god-tier engineers you have. So yeah it sucks that the game got out with these bugs, but take a goddamn step back and let them try and resolve it. Nobody died as a result of this release, so it's not a big deal. Once it's fixed I'm sure you can recoup that massive investment you put into the console and the game.
What you say about QA is true, but all of that flies out the window when you are forced to release the game before the holiday season begins because Microsoft is trying to fire all of its cannons.
There is no real excuse for such a broken game of this magnitude otherwise.