Board Thread:Naruto Discussions/@comment-1783334-20150430232848/@comment-1018594-20150501035145

Probably because the face replica isn't laughing like a derp.

In the anime it's not really clear, but manga-wise the resemblance is there, in some panels more than others. Especially when it was first seen on Danzo's arm and Madara's chest, when the emphasis was on the fact that they had Hashirama's cells.