and the lakers traded vlade divac to get him, so your point is still valid. that sounds to me like a scouting/management issue. sure, that just happens sometimes, but it seems to be an overall theme in west v. east.
like centerz mentioned, there is an "arms race" feel to the competition too, with west teams loading up for the last however many years to compete with each other. teams in the east just can't get it together. also, for a long time, the east was the "more physical" conference, where the west was more finesse (offense oriented). the way the game is officiated (less handchecking, etc) has benefitted finesse teams more than those geared for banging and defense.
some of the spurs' success can be attributed to their international scouting, too. ginobili and parker were spotted overseas and deemed high priorities.