i dont believe this is the case, they haven't sought to protect the image so it loses the trademark protection. if they even applied for it back then, which is unlikly. you'll recall that Arsenal changed their logo a few years ago specifically to be able to protect the new one and stop the tat merchants copying it. the club have no right to the term "seagulls" in relation to football unless they have registerd the trademark, and since its been in use for so long as nickname i dont think it would stand up anyway.
I agree to a point, and I can see how it can be defended, but if the club wanted to seize the opportunity to fight it then they might. They'll think they have a case given the nature of their business. They can point to their core business being threatened and they will want to protect that business.
If you're selling brands and naming rights, basically you know as well as I that the owners of the brand will wish to defend all the territory. If that's a path they want to pursue.