I think most sites thanked the skinners who represented them.
As for the approval, the way I see it myself, you are making a skin in the name of a site, therefore, it affects their image.
So, for example, Velocityart would have legitimate reason to not want me to represent them with a skin they disagree with (for example if the skin used porno or violence, or if they just thought if was just too ugly.
Of course,t hat's the way I personnaly see it.
In my eyes, common politeness and decency had 2 parts:
- the skinner should show the skin to the site it represent first
- the site should thank the skinner
Not everyone can agree, but that's how I see it.