Tim Duncan isn't the best player on the Spurs but he is the face of their franchise.
Just like Paul Pierce is in Boston and will continue to be.
Who is the replacement option?
They don't have one. The Celtics have an All Star replacement, his name is Rondo.
I'd also argue that Ginobli is the face of the Spurs now. (just before his injury this year).
Pierce is the face to Celtics fans, particularly long time traditional fans.
Again, ask yourself who the face of the Celtics to the general public is in 2012?
Is it really that hard to take of the green glasses guys?
I can see the argument that Rondo is now the face of the Celtics franchise, though I don't think the franchise truly has a single "face" right now. And actually, I don't think it has since 2007. Until then, it was Pierce. After that, it was collectively the New Big Three. I agree that as Celtics fans, a lot of us held - and still hold - to the idea of Pierce as the face of the franchise because we were so happy to see him get his chance. But KG was the force that instantly made them championship contenders. Still, because of Pierce's longevity and skill level, KG couldn't just take over as the face of the franchise - it was instead all three and the team concept that fit in so well with the franchise's history and legacy.
But with age and injuries, and Rondo's emergence, there has been a change, and Rondo at least would have to be included with that "face" group starting in 2009 or 2010. Now, the aging has gone so far that I think if there was a face, it would be Rondo. Cs fans and the organization might still say Pierce, but I don't think you can control who the face of your franchise is unless you're pushing that through the media. The term "face of the franchise" implies imagery and representation, and that typically occurs through the media. And as has been said accurately, the media last year and this year adopted Rondo as the symbol of the Celtics.
That said, I think Rondo is held back from face of the franchise status by all the trade rumors and the national and local perception that some people in Boston want him gone. Hard to say you're the face of the franchise when everybody is talking about trading you in your prime not to get more pieces for a run now, but to rebuild.
However, now that my two cents are in on that, the argument that I do not think can be made is that Manu Ginobli is or ever could be the face of the Spurs. Tim Duncan is on another level of greatness. It took getting at least one better player on his roster for Pierce to win a championship after a decade in green. And while he won the Finals MVP, he was the second best player on his only championship team, the franchise's 17th. Tim Duncan was the best player on four championship Spurs teams, including one in his rookie year, the first in that franchise's history. Tim Duncan was a two time MVP, perennial All NBA player, the greatest power forward ever and one of the ten best players in NBA history. Pierce is a Hall of Famer, but has never been in an MVP discussion and has never even made one All NBA First Team. Duncan is easily the most important and best player in the history of his franchise. Pierce is arguably top five in his own franchise's history.
While I love Pierce, all of this is simply to say that it was and/or is not that big a deal for Pierce to be overtaken as the face of his franchise while still playing, indeed while he was still arguably in his prime. But for ANYBODY to take over as the face of the Spurs while Tim Duncan is still playing, he'd have to be a superstar. That's not Tony Parker or Manu Ginobli (nor could Rajon Rondo overtake him).