Siannah: “There’s one more key aspect about trade marks you need to know: once you have one, you need to enforce it.” Otherwise, as was the case with Hoover, you might end up losing it. Bethesda may not even want to do this, especially as suing indie’s golden boy is hardly the way to earn gamers’ love – but they may feel they have to.
A trademark is effectively lost if its use becomes widespread enough that the mark can be considered to have become generic (also known as dilution). That's a big part of where the importance of defending a trademark comes in. However, I think it would be difficult to argue that "Scrolls" conjures up "The Elder Scrolls" to a sufficient degree that any meaningful dilution would occur in this case (particularly given that there are plenty of other variations on "scrolls" out there as the names of other products, each with their own trademarks). On top of that, defending a trademark does not require sending a C&D or filing a lawsuit; another perfectly valid way to defend a trademark is to claim that you believe your mark is being infringed upon, but are willing to license that use of the mark for some token amount (say $1), along with stipulations that the mark not be used in certain ways (such as in conjunction with "elder"). Trademark defended without being a dick.
No, in the case of Bethesda going after Notch I'm pretty sure it was just a case of them not keeping their lawyers on a short enough leash then not wanting to back down once things got started (it seems many lawyers believe its their solemn duty to be incorrigible sons of bitches whenever the law allows them to).