Someone once pointed out the genius of hiring them.
If Obsidian did bad, then Bethesda could say "look, see what the original creators did? Fallout is better in our hands now." The game being bad, they can say "hey, the fans wanted an original fallout" and simply give Obsidian all the blame.
If Obsidian did good, now they have an example to follow AND Bethesda looks good for hiring them to begin with, as it was a wise decision and they listened to the fans.
It's a win-win.
It is a wise decision in that respect, but I have a hard time believing that Bethesda really cares that much about us (that is the small number of fans who really care about the series) when compared to how much they care about sales with (what I believe to be) the large majority of fans who are "casual" fans. These "casual" fans really don't care about the series being an RPG series, rather they enjoy exploring the map and blasting people's heads off with overpowered weapons, and there's nothing wrong with that, except that they make up the majority of gamers today, and, as such, force developers to make "dumbed-down" games in order to sell more copies. My point is that Bethesda probably (and understandably) won't cater to us in future games, but rather to the larger audience which will make more money for them.
I'm just glad that Obsidian
did develop New Vegas and that we got a truly great Fallout game out of it.