We don't really look at our leaders as actual heroes anymore. I also want to point out that there is an element of the fanciful here too. It is not just time that's passing. Our leaders are not going to need to slay monsters. That being said, we do expect our leaders to slay metaphorical monsters. We want both of them to be brave and know how to act in a pinch.
How are Hrothgar and Beowulf different than today's leaders, you ask. Frankly, I'm not sure Hrothgar is so different from many of today's leaders. Perhaps I'm too cynical, but I see Hrothgar as a sometime-hero. When Grendel becomes the marauder and rampages through the country, Hrothgar appears to have simply retreated in fear for many years. He still puts on the show of power and honor during the day, but at night he leaves his hall in fear, waiting for someone to come to his country's rescue. That does not sound so very different from certain types of leaders today. Beowulf is arrogant and confident he can come in and take care of the problem with brute force, a tactic and attitude many leaders have. His motives do appear to be at least partially altruistic, for he did not have to come and he wants nothing but the honors due to someone who saves a country single-handed--literally.
It is interesting to reflect on the concept of honour and obedience in the current climate of whistle-blowing, when people are actually encouraged or praised for going against their leaders or superiors when it is a matter of the greater good. Certainly this is one element that you might wish to analyse and to consider in regards to how heroes are different nowadays.
You also might wish to consider what makes Hrothgar and Beowulf such heroic figures. They are based on traditional notions of masculine power. Certainly I think we have moved on somewhat from this point and now are open to heroism being expressed through less brute acts of violence and power.
During the time in which Beowulf was written (and the exact date, as well as the author are not known), honor was the most important part of the life of a ruler and his warriors. When this story was told in the oral tradition, the scop (storyteller) would grandly emphasize the bravery of a warrior, which was a part of his code of honor.
At one point in the story, Beowulf refuses to do anything that would displease his feudal lord. Beowulf is a man of honor and loyalty, with no regard for how his actions will serve him, but for the glory they will bring to the king (or feudal lord) he serves.
Hrothgar is also an honorable man. He honors Beowulf's family and the warrior's willingness to travel so far to help defeat Grendel, when he and his men have been unable to do so. When Hrothgar's favorite warrior, Aeschere, is carried off by Grendel's dam (mother), Hrothgar is devastated. The honor shown here is much like the Marine's code of leaving no man behind. Hrothgar will not give up on Aeschere, and Beowulf promises to pursue the creature that has taken him.
In comparison to our leaders today, it often seems that too many are only interested in obtaining fame and fortune. There is no sense of honor among many of our leaders who have become jaded by their years in politics, or who never meant to serve the people in the first place, but only their own interests. On occasion we will see someone with the same code of honor displayed by Beowulf and Hrothgar, but it is infrequent.
Perhaps the tone and mood of honor and loyalty are the elements that make this story so impressive and timeless. Our "superheroes" exemplify the same traits as Beowulf (and Wiglaf), as well as the leader of the Geats, Hrothgar. We wish for these kinds of heroes, as seen in fiction and movies made about great warriors, but we have difficulty finding such things outside of the realm of imagination. What we cannot find in the real world, we sometimes can only see in the world of imagination with some notable exceptions in the "real world."
If I were to identify heroes like Beowulf, they would not be found in political realms; however, men and women of valor and honor were present for the world to witness on 9-11. They were the stuff another world, and perhaps it was this sense that make them "larger than life" heroes, much like Beowulf.