The main difference between epics today and those of the ancient world is that epics used to be created around a grouping of ideas (or characteristics) in order to illustrate an ideal. For example, the epic of Beowulf was begun to illustrate the conventions of the epic, the epic hero, and the culture of the time.
This said, epics today tend to be defined after the fact. The epics come to be defined as an epic by the populace after its introduction. Now, while one cannot be absolutely sure that the ancient epics did not come to epic statue in this way as well, they are already identified as epics as modern readers are introduced to them.
When researching modern epics, a list of movies emerged. According to one site, the following movies are considered modern epics: Dances With Wolves, Malcolm X, Gone With the Wind, and The Godfather (only parts 1 and 2).
Another search found Frank Stanford’s "The Battlefield Where the Moon Says I Love You" as the most epic of all poetry in the modern era. While this may be true, how many people have actually heard of this text?
In the end, the audience is the greatest factor when defining the epic. Many of today's readers lack the desire to read long, extended tales which fail to hide the characteristics wished to be highlighted by the author. Our idea of who should be placed upon a pedestal differ so greatly that simple commonalities fail to exist. Today, epic heroes do not exist.
Therefore, modern audiences differ form ancient ones based upon the fact that ancient audiences shared the ideals for which their epics and epic heroes were based upon. Modern audiences, on the other hand, cannot agree on enough characteristics to define a true hero. In a sense, the multi-award winning, pro-athlete, who lives in a multi-billion dollar mansion, and whose face graces the pages of Vogue, Seventeen and Maxim fails to exist. Makes one think of Bonnie Tyler's 1984 release of "I Need a Hero."