Is there any overview / statement of which license is applied under which circumstances and why? Or at least some comment what is used for the newest stuff?
i think what you find looking closer is that the Arduino platform is comprised of software from many independent open sourced projects, Processing/Java for the IDE, avr-gcc for the compiler, avrdude for the uploader, others for the various core libraries, etc. So as the Arduion team didn't write all (or even the majority) of the software used in their distrubution I don't you will find any simple answer to your question.
Lefty