It's not Bethesda, it's Obsidian. They do this same thing with every game they develop, they're always a buggy broken mess.
Not necessarily, there are a number of factors that can lead to a buggy release. In the case of Fallout NV there are usually 3 entities involved in the QA process for a console release that should all share blame to some extent.
1.First goes to Microsoft TCR Compliance. A game has to be approved in order to be allowed to be sold to consumers. The requirements are cut and dry and if the game fails to pass it cannot be sold until all TCR requirements are fulfilled. I can't go into detail on the requirements since they are not known to the general public but you can get a general idea by checking out the game testing wikipedia entry.
2. The Publisher- Has the ability to postpone the release of a game due to the game having a lack of polish i.e (buggy). However postponement usually means a loss in $ due to a failure to project or estimate the time it would take to complete a project. The cost to run a studio can be fairly high depending on the amount of employees working on a title. Anywhere from 300K a month to multi-miliions. The closer to release the more expensive the studio will cost to run. Near the end of the run, contracted employees will be hired and even outsourced in order to get a game out on the release date.
3. The Dev Team- Dev teams have to stay honest with their publishers and let them know the true state of the game, and fight for more time if they feel the game is not up to par in its current state. I do know some publishers often ignore these requests and often opt for cutting content rather than improving what content is already there.
In general it seems like this all may be a business decision. They could have spent more money running the studio to get the progression stoppers out of the game, postpone the release, and miss the X-mas rush or they could ship it now and hopefully rely on x-mas shoppers buying presents for their kids hopping parents aren't gamers themselves and don't read reviews.