So far I have not yet once, or rarely seen, an author speak up and say "that's not YOUR theme all you did is was modify....blah". It's a very satisifying feeling to call a theme your own and I don't see any reason to villify or pick on those that simply change the header and call it their theme - why can't they? Suppose they keep the original credits, is it no longer their theme? If Kubrick is intact, for example, and the only thing that has changed is the header - it's a modified kubrik theme. Technically speaking, it is not the the same theme as it no longer has the blue banner.
It's a very interesting question to ask, but in my example I felt it important to credit the authors from whom I may have been inspired or used their works as a base template. What would be the definition of a style? Changing colours makes it a different style? Well..yes I think it does as it's a modified version of it's original form.
The question then is, how much is it modified - even if it's 0.5% as someone rather rudely explained to another user, it's 0.5% originality from that user and thus the user is welcome to credit themselves for doing that 0.5% as long as the original author is credited for the actual original. Isn't the link back and credit as important as the semantics of what is a unique theme and what isn't?
If I modified all the iamge sin kubrick to blue - would it wrong of me to call it "Sea Blue Theme" by Jinsan, based on Kubrick by Michael"? I don't think it would be. My only request would be that modified themes clearly identify the authors of the original content on their page - I say this because a credit in the CSS is not going to be seen by anyone else, and so for me, personally, it'simportant those that deserve credit are given credit publicly.