Hey boy get a sweater: Angus on NPR?
Here's the link.
There is much more than just the salary cap (which restricts teams' overall payrolls) involved in the financial hosing of LeBron. It's the whole collective bargaining agreement (CBA). Even if a team chooses to spend over the cap and pay the steep "luxury tax", there are still provisions in the CBA that limit the maximum salary any player can receive, how fast that salary can rise over the course of the contract, and how long the contract can last.
All of those things work against the LeBrons and in favor of the "median" player. Whatever sized pie is available, these other CBA provisions limit how much of it can go to the superstars, thus leaving more of it for the rank and file.