The word 'genocide' didn't even exist in 1915.
May be wrong, but I believe the world "genocide" was coined by a man in the mid-1940's in reference to this specific event, the Armenian massacres.
Personally, I chafe a bit at the double standard here; anyone these days who denies the Holocaust is hit with the "racist/bigot" tag, but it is OK to deny the Armenian massacre?
That being said, many politicians seem to tiptoe around China's atrocious rights record as well. Perhaps this is just the way things are now.