Bottom line is GPL allows for anybody to redistribute the theme/plugin in any manner they choose, free or pay. Support on the other hand is not covered at all in the GPL. So, paid support is appropriate. However, if someone exercises their GPL rights and redistributes a GPL product which they also paid for the support and updates say for a year, and then the developer terminates their support because of someone exercising their GPL rights, that developer would be required to issue a full refund. The other option would be they would get a chargeback which will cost more than the initial refund would have and if they get enough chargebacks, jeopardize their merchant account, or even get sued.

It is pretty simple. If you are going to develop for the WordPress eco system, those are your only options.

While this has been an interesting discussion, the point of denying GPL rights is moot...