I just read through the explanation provided in the (now closed) thread and I believe the source code should still be made freely available. Both GIMP and Blender are licensed under GPLv3, which requires full disclosure of any derivative work.
"GPLv3 adds more clarity with regard to what constitutes a derivative work. For example, GPLv3 states that if the program is "specifically designed" to work with a GPL-governed library, then the library is considered part of the overall work and the entire application is governed by the GPL. However, if one could swap out the GPL library for another library (i.e., if the application wasn't "specifically designed" to work with the GPL library), then it's not part of the overall work and would not be governed by the license." (~
http://www.ibm.com/developerworks/rational/library/edge/08/mar08/curran/)
Realbench was specifically designed to work with the GPLv3 governed applications GIMP and Blender, since it's not possible to swap out either and obtain the same application functionality.
Or am I missing something?