The reason it's one of my least favorite topics is that it doesn't really matter, or at least not as much as the media, the rich (but not super rich) owners, and other uninformed or interested parties would have us believe.
I shall be arguing as much as I continue this series (which I shall roll out at a bit more deliberate pace than my Game Time report). To whet your appetite, here's some interesting data on the disparity in payrolls across time and the four major American leagues. The chart below plots the inequality of payroll distribution in the NFL, MLB, NBA and NHL from 2000-2010. Payroll data from USA Today (except for the NBA 2009-10 season).
To measure inequality, social scientists employ what is known as the Gini Coefficient. If you want to know more about the math behind this, click on the link (which takes you to the Wikipedia page). For now, suffice to say that the Gini Coefficient increases as inequality increases; a sample with a Gini Coefficient of 1.00 would be perfectly unequal, whereas a sample with a coefficient of 0.00 would be perfectly equal.
As you can see, the MLB has consistently maintained a greater disparity in payrolls than the NBA and NFL since the start of the previous decade, and the NHL since 2005. Far more interesting are the trends of salary disparities in the non-baseball leagues. Before the 2004-05 lockout season, the NHL was maintaining a level of payroll inequality similar to that of the MLB. Pro basketball has also seen payroll inequality wax and wane through time, while the NFL's distribution of salaries remains rather stable.
Rather obvious here are the effects of different collective bargaining agreements (CBAs) on salary distribution. To make them clearer I built the following chart with different shades for seasons operating under different CBAs.
On the other hand, Baseball has operated under three separate CBA's, not one of which contained a hard salary cap. As a result, there's no significant difference in payroll disparities between the three different MLB CBA eras.
One can make the argument that the MLB's regime actually exacerbates payroll inequality. While mid-level teams can't afford to pay the "luxury tax" for multiple seasons in a row, the richest teams (specifically the Yankees) aren't significantly dissuaded from doing so. Moreover, the absence of a salary floor fails to disincentivize the hoarding of revenue sharing capital.
The chart above reinforces my analysis of the MLB's salary regime. Payroll data for the other leagues prior to 2000 is dear, but the data from the MLB indicates an increase in payroll disparity following the 1994 strike and the ensuing 1995 CBA. This disparity peaked in 1999, but has trended in a narrow window between 0.20 and 0.25 despite the imposition of a "luxury tax" in 2003. If there were any parties to the 2003 CBA who expected the luxury tax to improve payroll balance, by now they should be thoroughly disillusioned.
In the coming weeks, I will delve more deeply into the economic disparities visible across and within the major sports leagues, questioning whether these inequalities are pernicious as they pertain to competitive balance. Full disclosure: I'm a pro-labor Yankees fan, so you can probably guess where my opinions lie. That said, I shall do my best to present my findings without bias.