krismalone: I think that Watchtower has hidden a lot but this is not one of those cases. The brief is public record and can be read by anyone. Just because they don't advertise it doesn't mean that they are hiding that fact. Tons of people and organizations will make something public and don't advertise it.
Phoebe: You should read the brief yourself and see what it actually says. The basic idea that Watchtower was trying to say was that there is no difference between providing a message that is spoken and a message that is printed on a piece of paper. So if you are cannot tax the donations given in a religious building during a religious sermon than you shouldn't be able to tax a religious sermon that is printed on the page and is given to someone.
In the brief Watchtower repeatedly stated that they did not take sides with either party in the case but wanted to present how taxation would affect them and their adherants. it only brought up Mr Swaggert's Ministries once at the end to discuss the State Supreme Court's decision and barely mentioned the ministry at all.
But again you should read the brief yourself it shouldn't take more than 20 minutes to get it through. You can also read the full Supreme Court Decision and see what the Supreme Court actually ruled in the Swaggert part of the case.
As a side note, I am not sure if they would have been correct or not, but Watchtower would not have paid this tax but each individual JW would pay the tax from the donation. That would mean that each individual JW would have to register with the state board and any local agencies if a county or city also wanted to tax the literature. So each JW would have had to file a quarterly tax return and send in the money that way.