I don't know if the 2 superstars is a hard and fast rule. It depends on the competition in a given year, and on the level of talent of the A-lister. I think Lebron has the ability, in the right circumstances, to win a title basically by himself along with some solid supporting players. You give him, say, a Manu Ginobli or Steve Nash, and I think he has a very good chance.
Dwyane Wade was able to almost win single-handedly, because they played against less than spectacular teams in the playoffs including the Mavs that year in the finals. Tim Duncan has been able to do that, though he has needed B+ level talents around him. I don't think that Kobe has the ability to win on his own. He is a top-level talent obviously, but needs a Gasol or Shaq (in his prime) to win. Unfortunately, the same goes for my Hornets' Chris Paul. Without another great player to help out, he won't ever win the big one. But then, he's a point guard. Don't know of many point guards who could win the title without some grade-A help. Maybe Magic Johnson.