- virtual - pages, that admin manually added via "Add Section" toolbar button in catalog (have yellow icon in grid)
-
template - pages, that are created automatically during theme file scan to match any TPL file, that is present in theme directory (red icon in grid)
These are values of "Type" field on section editing page by the way.
The main difference between virtual and template type of sections is, that "template" type sections use each own TPL to show their content (and you can place m_RequireLogin on it safely), but "virtual" type sections all use the same template (called design template) to show their content, but each of the pages just have different content block data to display on it.
This way by placing m_RequireLogin tag on a design template you'll end up with all pages using it become login-required.
Dmitry proposition is to add "Require Login" and "Require SSL" checkboxes to section properties for user/developer to be able to specify these settings for each section individually no matter, that they use single design template to display their data.