The reason we use the current page skin for PageLayout.aspx is because it is needed to do this to solve a bug in previous versions.
Suppose you set a page to use a skin like ramblingsoul-5contentpanes which has the 2 extra content regions. PageLayout.aspx detects whether to show the extra content regions for adding content by the layout.master and whether the extra content regions exist. If we use the site default skin there then it will not see the extra regions and therefore not display them if the site default skin does not have the extra regions. So it was impossible to use the extra regions on the page specific skin unless we use the page specific skin when adding features to the page.