Exaggerating the numbers involved in a battle? I'm sure that never happens.
The Spartan Epitaph was written from the point of view of the soldiers who died, saying they took the orders of the Spartan government (primarily the Ephers) who had sent them to Thermopylae. Like Nelson, they could have said, "Thank God, I have done my duty." But that is less evocative.
I recall reading that in the military council on the eve of the last day of battle (before the Greek forces were completely entrapped) the Spartans announced that it is a strict law of Spartan warfare that they never abandon a post without orders to do so and since they had no orders from Sparta, they were obliged to stay.
Now, we may agree there is a strange mixture of the noble with the insane in this scenario. Certainly, our sense of humanitarianism, even in warfare, would never allow us to have standing orders which were in effect to commit suicide.
A curious parallel comes to mind: Bastogne, Battle of the Bulge, Christmas 1944. The Germans delivered the ultimatum in similar terms to that of Xerxes. Of course, we know McAuliffe's famous reply: "Nuts"! Were the Americans being Spartan, or did they trust that help was on the way and they had to hold out? I think it was a bit of both. They knew it might be suicide, but it was not sure. They likewise knew the critical strategic importance of holding Bastogne against the odds and that there were enourmous American and allied forces within striking distance. The question was, would they make it in time? Damn, I'm so proud of those men. Where have they gone?