Hi Tim,
I agree with you that PageSettings.aspx should use the site default skin when creating a new page. It correctly uses the page skin when editing an existing page, but it was using the home page skin when creating a new page as you pointed out, and that is a bug. I just fixed it in my copy so it will be fixed in the next release.
Most admin pages do use the default site skin, but PageLayout.aspx and PageSettings.aspx are intended to use the page specific skin, but you are correct that in the context of creating a new page PageSettings.aspx should use the site default skin.
Best,
Joe