Does this help answer your question...
http://www.arduino.cc/en/Main/FAQ
The two paragraphs containing the word "derivative" seem to be relevant.
Or this...
There is a discussion here about the USB IDs..
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1285500728/0
This may be too old but it should give you a feel for the Arduino developers' intent...
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1232672092