GPLv3 mainly added new clauses to deal with other "intellectual property" laws that people started using to "protect" their source code such as patents, TIVO-iz

GPLv3 mainly added new clauses to deal with other "intellectual property" laws that people started using to "protect" their source code such as patents, TIVO-ization tricks, and DRM. GPLv2 was written back when copyright was the only thing people were using to prevent sharing of their code.