Quest bugs can be forgiven I think. A complex quest will have lots of scripting and all it takes is for a dev to miss a trigger or a player to do something unexpected and the quest is broken.
Less forgivable are the engine crashes. These really need to be caught, especially in an RPG where you can lose many hours of gameplay.
And to pour a little cold water on the "at least they will patch it" argument - patches and DLC for Fallout 3 seemed to add as many bugs as they fixed. Certainly on the PS3 the GOTY edition was extremely bugged, and with bugs not common to the original.