> The wast majority of developers work at internal code, code that never will get redistributed outside the company walls.

According to my dictionary this means closed source, which only reinforces my statement.

As the developer, I can see the source tree. The company owners can see the source tree. As such, everyone who has access to the program also has access to the source.

GPL allows this, as do every type of open/free software license. Either this mean that your word choice of "closed source" lacks meaning, or we are not talking about the same thing.

If the source is not made available to your customers it is not open source.