huge differences between all of these: clyde/barkley/olajuwon were all at the ends of their careers when they were united. parish/mchale/bird - parish was traded to boston in 1980...mchale and bird were both drafted by the celts magic/kareem/worthy - kareem had arrived by free agency, but preceded both of the others....but magic and worthy were both drafted by the lake show pierce/garnett/allen - garnett and allen were clearly going as supplementary pieces well past their prime.
The only difference is team management put those groupings together. These guys were just smart enough to be free agents at the same time and a little lucky as well.*
All of these big 3's were extremely effective by the way - the best combinations of their time. Clyde-Barkley-Olajuwon barely missed going to the finals - had Brent Price not been injured they may have very well prevailed as he was critical in spacing the floor in Rudy T's system. Once they lost him they didn't have a 40%+ 3 point shooter and that was deathly as Matt Maloney was too inconsistent. The point is that assembling 3 stars onto one team can be done many different ways. Houston did it through trade's but they were effectively not much different than SnT's. Just like acquiring Pippen after Clyde. Let's not forget that Bosh and LeBron acquisitions were technically also trades.
just cut the nba down to 18 teams and we can have big 3s all over the place, combine all the texas teams, we can have the internation superstars of yao, dirk, scola, manu, and parker.