People don't want to see it any more, apparently.
Ninja Gaiden 3 won't feature dismemberment, according to Team Ninja. While Ninja Gaiden 2 saw enemies being sliced apart, the upcoming game apparently won't feature any slicing and dicing.
Speaking to IGN a member of Team Ninja said "we don't think people want to see that anymore," adding that "they've already seen it". This follows the toning down of dismemberment in Ninja Gaiden Sigma 2 - the PS3 version of the Xbox 360 game Ninja Gaiden 2.
Team Ninja has also confirmed that Ninja Gaiden 3 will include PlayStation Move support.