The Spurs do regularly pinch their pennies as much as possible; I am not sure they would be willing to dump a guaranteed contract for a better-seeming prospect even if one came along. I would expect the decision to be much easier for them if William's contract was not guaranteed.
In other news,
http://myespn.go.com/blogs/truehoop/...y-Bullets.html, "The Clippers gave up on Jared Jordan, trading him to the Knicks for cash. The Knicks now have 19 real deal players counting Jordan, and only 15 roster spots, so I'd say he's facing a stiff challenge in New York, too. There are a bunch of teams that will be making painful cuts in the weeks to come. (Detroit, for instance.) Teams with open roster spots are waiting ...".
In particular, I expect the Knicks to be forced to cut Demetris Nichols (#53, 2007). Judging on summer league, Nichols would be a huge improvement over Williams. He would be a good fit with us, a SF, shooter, and a willing defender.
http://www.draftexpress.com/viewarticle.php?a=2184