Those aren't warnings, those are threats.
A jihadist "warning" is a "convert or die" message.
In contrast, a jihadist threat is simply that they are going to attack. In their culture, these differences are not subtle for one thing and for another thing they matter.
Threats are common (e.g. "the Arab street will be enraged").
Convert or die warnings, on the other hand, are much more rare.
In either case, you'd be hard-pressed to show a warning letter to a U.S. President (or major Western leader) prior to the Beirut barracks bombing, Khobar Towers attack, USS Cole bombing, Blackhawk Down in Somalia, African Embassy bombings, 7/7 London subway bombings, Madrid railway bombings, etc. No warning letters. No video warning, either.
What you are doing is aiding Iran's bluff. By pretending that radical jihadists "always give a warning before they attack," you lend undeserved credit/legitimacy to Iran's intentional bluff in their recent letter to President Bush.
Don't do that. Do not aid their bluff.
OK. I do see this as a warning, even if they are rare. Is it helping the US to only ascibe certain meanings to this letter, when ALL possibilities should be looked at? It sure wasn't a peace overture, as the MSM portrayed it.