IANAL, but digging around your Wikipedia link suggests that the litmus test here is whether or not the material is to be considered "obscene". The law struct down in the case you linked was worked around by introducing the PROTECT Act, which clarified it as "obscene depictions" of minors.

This so far has not been challenged, as apparently the guy I mentioned in the Simpsons' case just entered a plea bargain:

http://en.wikipedia.org/wiki/Legal_status_of_cartoon_pornogr...