The difference between the Armenian Genocide and the Holocaust is diplomatic. Turkey considers itself the successor state of the Ottoman Empire and has never admitted that what happened was genocide. Germany, of the other hand, does not consider itself a successor state of the Third Reich, and condemns the Holocaust for what it is. As Turkey is a valuable ally of the west, nobody wants to piss them off. This could easily escalate into a diplomatic incident.

A society committed to the notion that government is always bad will have bad government. And it doesn't have to be that way. — Paul Krugman