This brings up some interesting points concerning the GPL.
Anyone who distributes GPL'ed code is within their rights to charge a reasonable expense to cover distribution costs.
Modified code, if distributed, must be made available to all and distributed under the GPL, which see above.
A basic tenet of the GPL is that charging for services (code modification, installation, customization, maintenance...) is always allowed, unlimited and between the buyer and seller. Capitalism at its purest.
So, no. The template author can not require payment to remove the link back in the GPL'ed version, but is entirely within their right to charge for software services or a non-GPL version of the code.
This may seem like circular reasoning and that the template author is now distributing the modified code, but if there are no other authors whose rights need to be considered, the author can choose any license or distribution method for the second version. The recipient is welcome to secure any one they wish to perform a similar service to the GPL'ed code.
member #798 - Free Software Foundation, http://fsf.org