Zodiaq~....both tact AND common sense is required.
Trust me when I say I have looked at many issues similar to this for many different people over quite a few years [even before Wincustomize.com] and there has been many quite justified complaints of blatant image use/theft which, quite frankly, this one is not.
Were the other skinner to have stated in his WB description that he was inspired by your skin or he even 'took' your images as a basis to work from/with, the resultant work is sufficiently different to be defensible as coincidentally unique.
It's not so much about how 'dissimilar' they are, but about how unlikely it is for them to be SO similar. There is a distinct difference in those concepts.
As for closing the thread....if it gets 'nasty' for whatever reason the comments will be removed, but we try NOT to remove threads if it can be helped....