I'm guessing it's active players, otherwise that list truly sucks. Actually it sucks anyway since they moved players out of position.
PG: I can see the Nash pick. Fisher, while clutch as a shot maker, doesn't tend to do much else. Nash tends to make excellent decisions down the stretch and has a knack for hitting big shots as well.
SG: Kobe's a good selection. I can't think of anyone else in the ball-park outside of Wade, and while he's a great late-game performer, Kobe's done it for much longer.
SF: I've seen him hit a ton of game-winning shots, which have been really great looks created by his teammates. I can't think of anyone better though. He makes the shots he gets, so assisted or not, there's no one better at his position.
PF: I don't know who I'd go with here. Duncan isn't all that clutch, to be perfectly honest. He's had some huge performances, but I did a project a while ago where I looked at players numbers in the last 5 minutes (playoffs only) and his weren't too hot (Ginobili's were stellar though). I don't consider Dirk particularly clutch either. I guess it probably goes to Duncan by default because who else is there?
C: Well, not Dirk since he's not a center. Definitely not D12. Yao might be clutch if he weren't injured by the 4th. Ilgauskas?

"Imagination will often carry us to worlds that never were. But without it we go nowhere." - Carl Sagan