Ok, in Don's defense, he only asked, and when I said I didn't like the idea of it being a paid WB skin much, he did say that he would be totally ok with someone else doing it if they could do it faster than him.
This said, I do agree 100% with your reasoning. When Don asked if he could make a Master skin out of it, I immediately felt uncomfortable with the idea but I couldn't pinpoint exactly why. So I told him it just didn't feel right in this case, mainly because Winstep, despite having paid for it, was never-the-less making it available to Winstep users for free.
The other reason, now that I had more time to think about it, is because this really is a Danilo skin and it's my personal opinion that Master skins should always be original skins, not derivative work (but I could be wrong, and there are probably exceptions).
Even though it was commissioned by Winstep (and therefore belongs to Winstep) it is Danilo's creative mind and skinning genius that are 100% behind it. You will never see me take credit for something that is not my own work, which is why his name is mentioned first place in the theme's description and not just 'Winstep Software Technologies' (even though the skin belongs to and would not exist without the latter): all WebGizmos and I did was put together the various pieces of the theme Danilo created in a way that could be used (as intended in the first place) by Winstep applications.
Now, WB ports of this theme - or any other ports - aren't really my concern for obvious reasons, but I don't mind them at all. Quite the opposite in fact: I think good themes should be shared.
So, anyone who wants to make ports of this theme to any other application and upload them to Wincustomize has my authorization to do so. No need to ask anymore. 
I can only hope Don doesn't get upset with me for bringing this out into the public - in retrospective I should have asked him first.
