Not many people can pull off the games Bethesda has made. It's like they have the secret ingredient in making a good 1st person RPG.
I love all of Bethesdas games... I really do. However, I think Bethesda fans get a little ahead of themselves when they say things like this. There are a ton of other very talented, and very capable development studios out there that could certainly do just as well, if not better making games then Bethesda. To act like they are the only ones capable of making a game like TES, and making it good, is no offense laughable. The problem is that most studios opt for cheaper, quicker, and smaller projects... so there is little to compare TES to.
There is one very simple reason why other studios do not make games like Oblivion/Fallout. They take several years, and a whole lot of money to make... and with a new IP there is no promise the game will be a hit. Studios generally are not going to put 4 years of work and millions of dollars into a game that has no promise of selling big. Bethesda on the other hand, has a very large and loyal following. Anything they make will sell millions of copies and be a commercial success no matter how good or bad it is (not saying anything they have made has been bad to date). That gives them the freedom to make games like this, that most developers/publishers do not have.
Eventually there will be a TES style game out there. Its only a matter of time to be honest...