Leading from the front is still a widely-used practice; duels between leaders to settle the affairs of nations, not so much. I blame artillery.
Imagine Napoleon trying to arrange a battlefield duel at Waterloo:
"I say there! It appears as if some wee dot over there is advancing towards us! It could be Napoleon, riding forward to deliver a challenge to our generals to settle this whole dreary thing with a bit of the old sharp and nasty, what?"
"Oh dear; Battery 5 opened fire along that lane a few moments ago, sir. The fuses were so nicely timed, but what of the honor of the army, should one..."
<puffs of black smoke appear 100 meters in front of Napoleon and his seconds>
"...detonate early? Oh, dear."
That is why generals don't fight duels any more.
It's really too bad; I think I speak for a lot of people when I say I would have paid good money to watch the Allied commanders fight Osama and the Taliban's leadership with steak knives on TV to settle who got ownership over the miserable countryside that they currently dispute via ambushes and robotically-controlled death machines instead.
Modern warfare's sheer distance makes it impractical and nobody is dumb enough to agree to fight a duel whilst surrounded by the other guy's machine guns.