So, a given "specification" (how a font looks to the human eye) can have many different "implementations" (ie. TTF files). The specific "implementations" themselves can be copyrighted, but somehow not the "specifications"?
If so... assume one TTF file which is copyrighted, pay-per-use license. Assume another TTF file, which is open-source, free to use and redistribute. The files both implement the "Helvetica" specification, rendering the same letters to the human eye. How "different" must the free implementation be from the paid one, for it to not be considered an infringement?