I tried to follow links to find out how the authors determine "wins produced" but the only explanation is that it is mathematically based (duh!).
I found this at the top of the table.
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Value of a Win = Total Payroll in the NBA divided by Number of Regular Season Wins for All Teams
Difference in Values = Value of Wins – Salary 06-07
Salary data from USA Today
Value of Win set at $1,478,280
WP48 = Wins Produced per 48 minutes