It was made using the oblivion engine and yes I know it's not as simple as that, I loved Oblivion and it had occasional freezing. Oblivion's freezing was acceptable, but Fallout: NV's issues are not acceptable. It doesn't matter if Obsidian made it, a publisher should stand behind a game even when flaws are present.
Yes,it was made with Oblivion's engine,but that doesn't mean Bethesda has to answer for the poor optimization work Obsidian did with New Vegas,i know it from personal experience,New Vegas is one of the few games that i had to stop playing altogheter cause im still waiting for them to fix it properly,and sadly we cant put the blame on publishers,if we could companies like EA would be ruined (I know,one man can dream right?) .