The difference between Presti and the Spurs front office is that Presti has had a bunch of lottery picks, include no. 2 Kevin Durrant to work with. The Spurs, on the other hand, are limited to late first round picks and second round picks since Tim Duncan (whom we were very fortunate to get).
It's only logical that eventually the Spurs would run their course and deteriorate. Yes, its tough to watch, but no tougher than watch the 80s Celtics and Lakers teams deteriorate and get run by the younger NBA compe ion. Same thing happend with the Bulls, who disbanded before things got ugly, though we have a hint of how bad things would have gone with seeing Pippen in Portland and Houston and Jordan with the Wizards.
Give Pop and RC the same tools Presti had, and they would have done equally well. As is, Spurs front office is the best in the business at putting together contenders on late first round picks and cheap signings. Good thing for us.
As a side, Phil Jackson is leaving the Lakers when it is obvious that they won't contend anymore. But he remains open to coaching a different team (I'd say Miami so he can yet again coach the best players in the league). Good thing Pop and R.C. aren't opportunists like Phil or the Spurs would soon be run by the Kevin McHales and the Isaiah Thomases of the world and everyone here would respect R.C. and Pop a lot more.