50/50. Дистрибутив попадает под определение "aggregate".

Т.е. они должны выложить исходники только GPL-софта + свои патчи, но это не затрагивает их компилятор, например. Да и другие дистры часто содержат закрытый софт в том или ином виде.

A compilation of a covered work with other separate and independent works, which are not by their nature extensions of the covered work, and which are not combined with it such as to form a larger program, in or on a volume of a storage or distribution medium, is called an “aggregate” if the compilation and its resulting copyright are not used to limit the access or legal rights of the compilation's users beyond what the individual works permit. Inclusion of a covered work in an aggregate does not cause this License to apply to the other parts of the aggregate.

http://www.gnu.org/licenses/gpl.html

http://www.gnu.org/licenses/gpl-faq.en.html#MereAggregation