[rdtsc]

Wait I think we are getting confused here. What code are we talking about here.

Copyright of code belongs to the author of the code, or a company that employs him.

If they took say GCC and then replace copyright notices on it, it doesn't become their code, they are using it under a license from the original authors. Replacing a header in a file doesn't magically give you complete control and copyright over it. That would be silly and it would nullify most of the open source software licenses.