It's a fair question, but there is a pretty simple answer. Linux is open source. That means the source must be made available. That is a mandate of the GPL, LGPL, and many of the copyright licenses, under which the software is distributed. If they became tyrants a whole people would get up, walk away, and create a new project/fork. This is why there are umpteen Linux distributions even now. Fedora/RHEL, SuSE, Ubuntu, Mint, Slackware, etc. etc. If people don't like something, they go and do it themselves 'better'.
Look no further than when Oracle bought Sun. Sun was the primary contributor to OpenOffice.org, an open source office suite. Oracle, after making the acquisition, tried to do a lot of nasty business, and so the Libre Office fork was born. Fedora and most others now use Libre Office instead of OpenOffice.
http://en.wikipedia.org/wiki/Open-source_software
Any company 'selling' Open Source software is actually still distributing the software freely and instead selling support. This is Red Hat's model for instance.
http://www.pcworld.com/businesscenter/a ... _club.html
They can't hide the source. It's not legal.