NIN has some really great stuff, but I don't know if I would consider them industrial since they are (were?) so popular. 
Pssht, obviously if a band is popular, it 
can't be industrial.  That's just ridiculous!  You start thinking industrial bands can be popular, and you start thinking they have to be good!
I have misplaced my words. Trent knows a thing or two about how to write pop music, and I think that his group exists on the border of the industrial genre. I am not seriously into industrial music myself, but I have several friends who are, and NIN is really mainstream compared to other sounds.
I didn't mean to imply that things can only be "cool" if they are "underground" and all the other stupid quotation marks that go in that direction. However, that fact that he is popular reflects the necessary fact that he is composing music for a more general audience. People who care a lot more about music than I do certainly could come to the conclusion that this defines how well a group fits into a genre.
I like listening to NIN. I think Terrible Lie (studio version, not the live garbage) is one of their better songs. That was a really popular song at one time, and it is relatively traditional in its composition. The percussion is really the only element that defines it as "industrial." So I think the popularity of NIN, while it does not itself affect the genre identification of the group, DOES reflect more fundamental reasons why they might not be so easily classified. 
Sorry for the confusion.