The rumor is that Spurs wanted a big but was undercut by Utah. So they got a guard. Which is one guard too many!
Forbes play in SL is impressive because in the last game, he scored by getting contact instead of in the 3 point line. So that says he's got some versatility in his offense.
If you remember the last two SL leagues, Spurs played Anderson a ton. They are doing the same with Forbes, he looks exhausted out there but he still is able to put up numbers. In contrast, Spurs barely play Murray. He sat out one game and played only one half in the last game. Perhaps he's not healthy.
The next couple of days are going to be key. Spurs need to know if Simmons is signed. Ginobili may likely come back, heck if Vince Carter can come back then he is going to do the same! I am sure there's till that 76'er offer for him to play over there. The Kings have realized that you want to have your talent surrounded with vets for them to learn the game (Hill, ZBo and VC). So other teams are valuing that presence too and are willing to pay top dollar for 'the education'.