> So, under this definition, the GPL isn't an open-source license.
Untrue. The GPL does not "insist that all other programs distributed on the same medium must be" licensed in any particular way. [1] And the GPL has been reviewed and is an OSi approved license, which means its been found to be consistent with the definition by the people that wrote the definition. [2]
[1] http://www.gnu.org/licenses/gpl-faq.html#MereAggregation