It is very easy for someone to think that they own IP rights that they do not, in fact, possess. As a result the copyright statement that you see often is written by someone with no legal authority to grant the permissions that that statement grants.
If you are a company with deep pockets, like IBM, you are a more natural target for copyright infringement lawsuits than the person who made the mistake.
IBM knows this, and learned a long time ago to be careful about copyright issues. SCO is a non-issue for this. They were careful before SCO hit the radar, and will be careful after SCO becomes the crater that it so richly deserves to be.
Furthermore IBM far from alone. Go check out what is required to sign copyright over to the FSF. That isn't paranoia. That is just the necessary due diligence to be sure that you actually own the copyright that you think you own.