Spurs have started other guys at Center besides Robinson over the years. They were just scrubby, big-body guys like Nesterovic, Muhammed, Willis, Oberto, and Elson... so nobody remembers them.
I'd say Duncan has played Center since maybe 2007-2008. That was more out of necessity though, as the league changed, and it became all about spreading the floor and getting the rim (and the FT line). I mean, can you imagine an early 2000's Popovich team playing like they do now? Shooting all these 3's? Pop would probably have had a heart attack.
And I have no problem with Malone over KG. I just feel like KG has both the higher peak and better accolades.