The only way he gets $10 mil per anytime soon is if the Warriors or Sixers give him it. Will they? If they won't, maybe he does opt for the MLE with a contender, with the idea of hitting free agency in 2010. The Spurs can offer him a starting spot and all the minutes he could handle. What better way to set one's self up to hit free agency, in a summer in which a great many more teams will have large amounts of cap space, and with a team which will have the cap room to give him that $10 mil a year contract or help facilitate a trade to another team that will?
Those are the two main things going for the Spurs right now. If he comes to SA, he's still a starting shooting guard in this league. If he goes to a team like Boston with limited cap flexibility in 2010 and limited minutes, then he's basically setting himself up to be a backup for a long time with less of a shot at that big payday.