TrueHoop had an excellent article explaining why the NBA's position of pushing down salaries doesn't necessarily address the issue of competitive balance. One reason, well run teams spend more when there's a chance at winning, like the Celtics did.
What we've learned is that spending is cyclical. The smart organizations, like all businesses, try not to spend until they need to. As an example, the Boston Celtics' payroll the year before they formed their Big Three? It ranked 19th in the NBA. The year before that it was 21st. They lost over 100 games over those two seasons. The NBA might contend that the Celtics weren’t winning because they weren't spending. But we must be careful about confusing cause and effect here. It may also be the case that the Celtics weren’t spending because they weren’t winning. Why throw big money at free agents when it won't really move the needle for title contention? Perhaps it is better to keep costs low until you can swing a big trade or increase your chances to land a superstar in the draft (see: Thunder, Spurs, Bulls).
This is precisely what Wyc did too. I remember in the lottery days hearing him say that he would open up the checkbook when the team was ready to win, and that's exactly what he did.
The article also makes the point that the Celtics drafting did more to put them in a position to win than their spending. Go read the whole thing. Worth your time.