You are right that they are all genocides. To give a special name to 1 genocide ["holocaust"] implies that the people who were slaughtered in other genocides are somehow "less" worthy of mention...The Armenian genocide is equal to the Jewish genocide of WW2, both groups lost more than half of their population, and both were hunted down for religious and racial reasons. Yet most people will go "huh?" if you mention the Armenian genocide, its just not taught anywhere outside of select colleges.
That implies that either Armenians are not as special as Jews are, OR that the Armenian lobbying power in Washington/Hollywood/theMedia is weak as hell compared to Jewish influence in those areas [and of course they are!].
The reason we don't teach the Armenian Genocide is simply; it upsets Muslims, especially Turks, with whom we wish good relations. Sandeagle is correct that this should absolutely be taught; along with the Holocaust, slavery of black Africans, and our own treatment of Native Americans it ranks as one of the worst genocides conducted in modern (i.e. post-Renaissance) times. There is however one difference; at the time, the Armenians did have a homeland, albeit one divided and ruled over. Their experience was very similar to, though for some populations more horrific than, that of the Poles in the latter 19th and most of the 20th century. Jews on the other hand were uniquely vulnerable since they were minorities ethnically and religiously in every land, many of which cooperated enthusiastically with the Nazis.
I also agree with Wreckem that Soviet purges, especially Poland and the Baltic states, should absolutely be covered in any course on World War II and touched on in that section of any twentieth century history course. As should Japanese treatment of the Chinese. And discussion of our own interment (often to financial ruin) of Japanese or ethnically Japanese Americans should also touch on the 49% who were German, Italian, Hungarian, etc.