The linked discussion talks about a program for PalmOS which is GPLed (GNU General Public Licence) called PalmPDF. This is a modified version of XPDF and allows viewing of PDF files on Palm devices without Adobe's free client or Documents-to-Go.
The software is provided (for free) in source and binary forms on the author's homepage, however, recently someone based in Hong Kong has listed the program on Handango for $50. The author is quite miffed that someone else is benefitting financially, but according to the GPL - this is entirely allowed. In fact it would seem the GPL actively encourages this!! Many of the comments have suggested the author should have used a different licence and I agree.
The purpose of the GPL is free as in speech, not as in beer. The author could always sell it themselves but has chosen not to. Therefore someone (or many others) could choose to do so.
Link to the Free as in beer/speech version
Link to the Free as in speech version
Of course, the reseller (behind) Handango must provide the sourcecode on request and a licence with each sell to ensure they are above board with the GPL...