Important to note that the league office is the only one tax exempt, not the NFL as a whole. Any tax takings would be pretty slim, since most of the income is from dues and most outlays are for salary, overhead, and logistics.
I think I understand what AJ was saying in the previous thread, about the owners really controlling the amount they're paying into the league office, though I'll note that having the league office provides benefits beyond just pooling money and paying a toadie like Roger, so it's a wash as to whether they would require lower dues of each individual owner even if there was no tax-exemption.
The more important thing to note is that something like 70% of the capital is provided by the public, with a lot of teams having ultimately profited from public stadium subsidies (they received more in subsidies the stadium cost). Only the Patriots, Jets, and Giants subsidized most of their stadium construction through private funds. You can argue that this should require some sort of social obligation, such as we're seeing here with the Adrian Petersons and Ray Rices of the world, but without strings attached you're looking at a very similar situation that we see in the banking and agriculture industries and many others where risk and cost are socialized and profits are privatized.
