Cowardice on the part of whom? Cowardice on the part of those who issued the threats or cowardice on the part of Sony? Both?
Both obviously. The ones who issued the threats are cowards for doing so without revealing their true identities and hiding behind a computer screen. The people at Sony are cowards for caving to such threats even though all of the intelligence from the US government indicated there was no reason to believe that those that issued the threats had the means or the intent to actually follow through with the threats.