Here is a very intersting blog on how the defendants in the Betonsports prosecutions are attempting to use the WTO rulings and GATS treaties to show that online gambling by americans on internationally based sites has to be legal.
A number of caveats here, this argument hasn't been ruled on, the case is likely to proceed very slowly, and even if the defendants win, there will be no precedential value.
However the basic principal is sound, and would transfer to a poker context, so its interesting reading.
Link to article