The celebrated brothers have been fixtures at the festival on the French Riviera for decades. Jury co-presidents this year, they are leading a panel that includes stars Jake Gyllenhaal, Sienna Miller and Sophie Marceau.
Joel Coen, asked at a jury press conference about the recent surge of Internet-based film companies like Netflix and how they were changing the industry, gave a deadpan response.
"How do we feel about people watching 'Lawrence of Arabia' on their iPhone?" the director said, elicting guffaws from the audience.
"There's something special about sitting in a crowd of people and watching a movie on an 80-foot screen," he continued. "Nothing can compete with that, and that's something that film festivals like this keep alive."
The Coens may be out of tune with shifting viewing habits. Ethan also acknowledged that he hadn't watched a TV show "in decades" - but festival organisers seem keen to embrace new technologies.
On Friday, a key-note speech from Ted Sarandos, chief content officer at Netflix, will discuss how new ways of viewing films - particularly through Internet streaming services - are shaking up movie financing.
The Cannes jury is often tight-lipped, and Wednesday's press conference was one of the rare times the thousands of journalists accredited to the festival will speak with them before the Palme d'Or trophy is awarded on May 24.
Mr Gyllenhaal said he had been glad to be asked be on the jury because he was "thrilled to see films before anyone else and for free!"
Mexican director Guillermo Del Toro, who made fantasy features Hellboy and Pan's Labyrinth, recalled his first trip to Cannes as 'a time when I didn't have hair on my ears'.
The hefty filmmaker joked he had previously turned down a jury slot in the hope of losing weight to fit into his old suits. "But now I have no hope."
Other members of the jury are Spanish star Rossy De Palma, Malian songwriter Rokia Traore and Canadian director Xavier Dolan - by far the youngest at just 26.
Having actors and musicians on the jury was important, said Mr Gyllenhaal, "otherwise, you'd just have directors up here telling other directors how great they are, and we can't have any of that!"
The jury will pick the Palme d'Or winner from 19 international entries, as well as acting and directing awards, to be presented on May 24.
Joel Coen rejected the idea the jury had become film critics by taking on their judging role.
"We're not exactly critics here. It's not about 'we hate this'. It's about what do we really like, what do we want to celebrate?," he said.