Consider the following: What Jubal Quintus has done is not only completely harmless, in that he is not only not making a profit himself, but he is not causing any damages to a company with no product interest in the platform he is using, but it is also a form of free marketing. Other companies have, in the past, PAID talented content creators on SecondLife for the sort of brand awareness creation Jubal is doing for free. Take, for example, the Smokin' Aces game that ran wild through much of SecondLife's user database prior to the film's release. Not to mention development costs, Universal Pictures spent approximately USD$3,750 on prize money for the in-world promotional game, whereas Jubal's creations have asked nothing of Bethesda/Zenimax. A wise marketing department would, rather than allowing the company to attempt to bully an avid fan, seek to encourage Jubal to create officially liscensed merchandise to create the brand awareness and loyalty that, for great numbers of would-be fans of the franchise, is sorely lacking.
Finally, again to Bethesda/Zenimax, consider that the more fans are discouraged from supporting a franchise they enjoy and charish through shared fandom, the more anger and spite develops and ferments. While Fallout 3's eventual release is likely to have its share of illegitimate copies circulating the internet, it should be considered that every action such as this adds at least one more gamer to the group that would rather not pay such a company for a game.
Now, since I've created an account anyway, I'll likely be on the NMA forums more often, but first things first, I had to make sure Jubal knew he had some support, and I hope that my response will encourage some people to rethink their attitudes and lend him their own.