At the risk of sounding rabidly anti-Bethesda again, I agree with mogwins in theory but don't believe it applies directly to Bethesda.
Their modding support is good, but it's not excellent. (better than Fallout's, which also explains our slow progress. Some of the things modders have done with the game by now are amazing, tho')
On the other hand, Todd Howard seems to get pretty defensive about people modding his game and messing with his property, oddly enough, and certain modders aren't modders anymore but "hackers." I think Bethesda has a stricter view of what they consider beneficial modding.
And that's not nice, because their games really benefit from the excellent mods out there. A lot.
Also: someone noted Bethesda just has a seperate legal corp that spends its time hunting down stuff like this. That's very correct, that's often what happens with bigger companies, as they become more jealous of their property. Sometimes justified, sometimes it's just bad PR. In this case, it's mostly because Bethesda is owned by ZeniMax, and ZM is just an archetype evil corporation thing (run by people of the Democratic party, too. Heh)