Actually Nintendo had a copyright on Duck Hunt in the past... it was lastly renewed in 1992. It's true that they've recently been denied a renewal because it's a 'generic descriptive' instead of a (unique) name.

( http://tarr.uspto.gov/servlet/tarr?regser=serial&entry=77131612 )

Don't worry though, they probably will be able to get a copyright on Ultimate Duck Hunting (Wii) and I don't think people would think about any other company but Nintendo when thinking about Duck Hunt anyway.

Cheers