Yes, maybe sometimes they just take an open source code and REWORK IT, but that is like tuning a car. Using their time and knowledge.
They sell their knowledge, like lawyers do for example. Nobody is forced to buy their reworked software.
Only, the license of that Open Source code-base expressively FORBIDS not distributing the derivate work's source code.
Open Source doesn't mean "take it and do whatever you want". It means "take it and do with it whatever the license allows you to". Otherwise, it's simply theft. Certainly no one is going to sue him, but that's the same as stealing from a baby. Baby ain't gonna shoot you but you literally stole.
I dont' know about ccminer, but sgminer has it's own code, and opencl kernel files.
If he supplies his own kernel file, nothing in the miner source has to be changed.