you would think that but they made New Vegas a closed ending... even after all the problems fans gave them for doing that with Fallout 3.
If there was a big out I am sure they would make something.. like another ship looking for the first one that was lost.
the fans didn't give obsidian a hard time for FO3 ending, you seem to forget that obsdian didn't make FO3, so the ending is an obsidian decision, not a bethesda one, obdisian had free reign to make new vegas they way they did to great extent, even if obsidian didn't have the game end, there's not enough content in the game to give you a reason to keep playing, its just a desert, there's not much in it, certainly not anything to explore other than a a few shacks. so its prob better new vegas has an ending, leave the non endings to games like stalker, oblivion, mass effect and FO3, those games gave you a lot more adventure to give you a reason to keep playing but not new vegas.