No it's not Obsidian's fault. The engine was very buggy to begin with, heck I felt that Fallout 3 was buggier than Alpha Protocol.
That's nonsense. Oblivion and Fallout 3 are buggy, so are all Gamebryo engine games - but NV takes it to a whole new level. There is NOTHING in any of those games as bad as any of the MANY game breaking bugs in NV.
Bethesda has to take some of the blame, but Obsidian is NOTORIOUS for releasing broken, buggy messes.
Kotor 2: broken buggy mess
NWN 2: broken buggy mess
Alpha Protocol: broken buggy mess
NV: broken buggy mess
They have very active defenders, though, constantly blaming others for their laziness and incompetence. Obsidian is a joke developer is what it comes down to.