When a user restricts the view to a page he owns so that he is the only one to be allowed to see it, the administrators can still get access to this page if they know the URL or following a link from another page.
However, this page will not appear to the administrator in the Recently Updated nor from the Browse Space views.

This is inconsistent.
I would expect a system administrator to have all the permissions on any page of the system and a space administrator to have all permissions on the pages within his spaces.