In a more perfect world, yes, I agree with you. however, the simple truth is, we do not live in a perfect world. A 100% bug free product is unattainable, in truth. there will always be *something* there, it simply comes down to a matter of whether or not it affects the gameplay. A "shippable" product, ideally, does not. However, stuff can still slip through the cracks--
As such, the ability to patch them when they DO arise is one of the benefits of XBL. People seem to think devs have this complacent attitude of, "well, there MIGHT be summore bugs left, but we can fix 'em later if we want" and that's patently false, in the console world. Hell, even PC developers bug test games to the best of their ability before releasing them, because it means wasting less time on a completed project. Bungie, and any other developer out there worth their salt try to avoid such issues if at all possible, because it reflects poorly upon them and their work, and that approach simply produces bad games.