Good article. With Brazil's economy booming, they can hold on to their great players longer and even bring back currently great players by offering them huge salaries (Fabiano, Ronaldinho). They can even buy great Argentine players (Conca, D'Alessandro). They also have a huge population and can withstand losing lots of their players.
Argentina is poorer these days in many ways, and the player salaries are very low there. Any decent player leaves, and there are no longer any good teams (even though the bottom half of the table is always full of decent teams). Even the big clubs have a lot of financial problems. And since they are a less-populous country (and it's so concentrated in Buenos Aires), they can't really get rid of all of their top players and still have a good league. Like Portugal and Holland, they can produce a few great players, but they don't have the depth to be able to sell them all and still have a good league. Brazil, with its huge population, can though, and they are becoming an economic superpower. I expect the Brazilian league to dominate South America in the next few decades and surpass the Argentines in terms of Copa Libertadores won (they're 8 down, but they'll catch up soon).