If there is anything that separates contenders from pretenders, it's the possession of an edge, or a killer instinct if you will. Championship teams had that mettle - teams may have all the talent in the world, but without it, they tend buckle under pressure, as the 2011 Heat will tell you.
Looking at the Thunder and the Lakers, one thing leaps out at me - their rosters have guys who are willing to do the dirty work and supply nasty to Pop's delight. Kendrick "leader in league scowls per game" Perkins, Metta "the Artest formerly known as Ron" World Peace, and so on. The championship Spurs had guys like Bruce Bowen, who wasn't afraid to get into the opponents' jerseys and even trip up jumpshooters as them landed. Even Robert Horry, known more for hitting clutch shots, arguably turned a series when he hip-checked Steve Nash into the scorer's table. Basically, an enforcer or a physical player whom fans of other teams love to hate, and I don't see one on the Spurs roster. Some people would point to Stephen Jackson as an example, but he's a boy scout when wearing the silver and black.
Teams that rely on finesse can go far into the playoffs, but someone with grit and nasty would be a good choice for a 15th man. No point in working out washed-up folk like Josh Howard or Tracy McGrady when the team needs someone with mettle and to protect the star players whenever things get ugly. I'm not suggesting that someone like DeJuan Blair better polish his elbows or something, I just hope that the Spurs better get ready to be more physical if they want to win the games that matter the most.