If Jagex were to even consider sueing for RWT, then they'd have to report over thousands of different people a day. Not worth it, especially when a majority don't sell in the masses.
For them to even consider something even remotely similar to sueing, you'd have to be extremely well known within the RS community and making an extremely large amount of profit on a regular basis.
RWT is 'illegal', in-game. A court case and a study or ANYTHING of the sort won't ever be conducted because 'imabot5395' sold 20m's worth of gold for $20 two days per week.