I'm not sure it's really that much the case anymore that linux is built by people for people, maybe it's still the case for debian as they are hard lined on the free software license issue, but most distribution are becoming more corporate, like firefox, and lot of development is paid by companies for the industry :)

But it still remain open source, and all the code can be re used freely or modified to build other open source software, or to patch bugs, or customize some part of the code, as long as all modification and distribution based on gpl code remain gpl and open source too.