Because one is a legal term entitling the offended party to petition the UN, the other is sympathetic but un-actionable.
Petition the U.N. for what?
Bush's use of the word "tragedy" somehow prevents the Armenians from seeking some form of redress for what happened in 1916?
Is it no longer permissible for Bush (or anyone) to refer to the Holocaust as a "tragedy"?
And who is the "Cihan News Agency", anyway?
Just because Bush is not in lockstep with you and the Cihan News Agency in screaming "genocide", does not imply that he believes said genocide did not occur.
All genocide is tragedy, yes?