I see a lot of people saying this but the only thing that stopped the Spurs from opening up cap room this summer was winning the 2007 championship. If they wouldn't have won it all last season, this would be the summer major caproom would have been opened.
After the championship, the Spurs did the following: extend Bowen's contract, re-sign Oberto, re-sign Bonner, re-sign Vaughn and sign Udoka. If the Spurs hadn't have won a championship since 2005, no way the Spurs do all that.
But looking back on it, did the Spurs make the right choice? I'm not convinced they did. If they would have followed through with the 2008 plan, the Spurs would have ~$8-12M in caproom right now. Obviously, there's no guarantee that all those players above would still be with the team but imagine how nice it'd be to have all that money this summer. The Spurs could have the Big Three and add another star. Bowen would have stuck around one way or another.
The 2008 plan was real but the Spurs decided to postpone it. Looking back now, it could have very well have been a mistake. Letting players like Oberto, Bonner and Vaughn walk to open significant caproom could have paid off nicely.