Like Marks said, he doesn't have a no-trade and is under contract for multiple seasons, so they don't have to kowtow to him.
Why would Aldridge and Murray make Spurs a front runner? Cavaliers' primary focus for the next year, is going to be doing whatever possible to retain James. Aldridge is a poor offensive fit with him and would likely leave in a year and Murray isn't ready to contribute to a team with championship aspirations or a good enough prospect to be the key piece in a trade for a player of this caliber.
Spurs would need to turn Aldridge and Green into quality assets, then re-route those assets, along with Murray and probably a pick, to get in the game.
Even if it were possible, I doubt they have the balls to gut this team at this point or trade Mills (eligible December 15th) when Parker get's back to clear up the PG logjam.
Heat have the balls and of the 4, the best available assets.