I disagree that the USA doesn't produce natural football-playing athletes. They just all grow up to play other sports that pay better.
Randy Moss as a striker? LeBron James patrolling midfield? Reggie Bush... anywhere? If we had a culture built around football rather than American football, I think we just might have won a World Cup or three.
Now, granted, some of our stars would curl up and die on the pitch (Peyton Manning, C.C. Sebathia, Tony Gwinn), but in a world where our Big Three sports never existed, I don't think Landon Donovan would ever have made it to the pro level.
American sports tend to allow for specialization to a degree that few others do (possibly Cricket? I don't know how that one goes). C.C. Sebathia can throw a ball 90 feet to a spot where he knows where it is going and you don't. Tony Gwinn could see what that ball was doing in flight and hit it into a spot where other players couldn't get it. Barry Bonds replaced his blood with pure rocket fuel and sent baseballs into orbit. Peyton Manning has a cyborg brain that figures out what 11 opposing players are going to try to do, and then throws a ball where none of them will be. American football positions have evolved to the point where humans without specific attributes simply can not play them. You must weigh 290+ pounds to play on the offensive line. You must be at least six feet tall to play the Quarterback position.* You must be able to run 40 yards in 4.5 seconds or under to play wide receiver or defensive back. You must be made of scrap iron and anger to play fullback.
Football has different skillsets for different positions, sure, but everyone needs to run, everyone needs to have ball skills, everyone needs to be accurate passers. You can have standouts, but no one aside from the Keeper (or Henri) is going to do something that nobody else on the pitch can do at all. If you don't know the game, you probably can't guess what position someone plays just by physical attributes. Heck, aside from being enormously, spectacularly fit, few footballers would stand out in a crowd of similarly-dressed people.
And then, yes, there's the fact that there's no discrete way to slice up a game other than minutes or penalties, and this makes it difficult for media to cover them. American games rarely have more than 60 seconds of continuous action before the play definitively ends. The spectacular plays can be distilled and described in a sentence or two. Popular American sports have been born of and shaped by the rise of the media that covers them -- baseball gave birth to the sports writer and, later, the live radio broadcast. American football began its growth on broadcast television and still drives the industry today. Basketball practically couldn't exist without television. All three sports have natural breaks in the action that allow for review, analysis, and most importantly commercials. All three lend themselves to highlights and sound effects and music videos and rock 'n' roll. There's the Shot Heard 'Round the World, the Immaculate Reception, The Catch. Hill to Laettner. Bill Buckner. Jordan's game winner in his last shot as a Bull. The Music City Miracle. Kirk Gibson. Willis Reed. Flutie's Hail Mary. These moments live forever, and they're complete. Self-contained. Discrete. It's much tougher for that to happen in football, unless it's a PK or corner.
Also you can't watch football games without those godawful droning horns now.
*Some people have claimed that Doug Flutie played quarterback, but since it was for the Bills no records exist of it and thus it is classified as a rumor.