I'd call it a minor foot-fault—a Serena Williams-at the-U.S. Open foot-fault, if you will (minus the explosive reaction). Tennis is void of aggressive and eccentric personalities at the moment, especially now that Novak Djokovic has calmed down, cut out gluten, and risen to within a hair's breadth of the No. 1 ranking. And Federer and Nadal, the current kings of tennis, have led relatively pedestrian lives for global celebrities of their stature.
But the casual sports fans you mentioned are no doubt domestic, and U.S. fans are down on the game because American tennis is at its lowest point in 50 years, especially on the men's side. If Ryan Harrison becomes a perennial Grand Slam contender or Andy Roddick or Mardy Fish can turn back Father Time to win a couple Slams, the griping about tennis lacking personalities will become a barely audible grumble.
As for the boring nature of tennis stars, I blame Pete Sampras. The GOATBF (Greatest Of All Time Before Federer) has about as much personality as an octogenarian line judge. Between his vacant on-court stare and his low-grade voice immodulation, Sampras took the fun out of each of his 14 Grand Slam titles and spawned a generation of listless, uber-talented tennis drones.
Hampton, care to weigh in?