Hi,
I've debated about this with myself as its also a usability issue if you make it easy for a user to create a page that might be invisible. Then I will be answering posts about why did my new page disappear?
See, if the child page is not in the same menu then it will appear but if its in the same menu it will not be visible if you create a benenath another page that is not visible in the menu. Many of the skins have split menus where the top menu is horizontal and only shows one level and there is a PageMenu that starts at one level beneath it. So in this case you can make home invisible and its children would show because of the split menu, but if the parent page is already in the lower menu or if you use a skin that does not split the menu or any skin where the child page is in the same menu as the parent, the child page would not be visible. To me this would be more of a support issue than the occasional person noticing that they have to make a page visible before adding child pages beneath it. To me it seems like its better that an extra step is required before you can make a child page beneath an invisible page, at least this way its clear to the user that the page they are trying to use for the parent is not visible.
Best,
Joe