Svetoslav , thanks for the suggestion. At this point, its clear that the IPagePreRenderCompleteEvent event is NOT fired when a page is either previewed or being edited via http://your.website.com/page-name/Action/Preview or http://your.website.com/page-name/Action/Edit respectively.
This is obviously not a caching issue either since completely disabling the cache via the advanced settings has no apparent effect. In addition, it stands to reason that if you are editing a page via .../Action/Edit, the page itself would not be cached since there are tons of controls, and what not, loaded into the page for editing purposes.
My guess is that the IPagePreRenderCompleteEvent event is not being fired because the page is not truly being loaded into its own context, but rather, its being loaded within a different context via the in-context page editor for editing purposes. Perhaps another similar event would suffice for this purpose. I do realize, however, that such a change wouldn't happen just because one developer wants to enhance the page editor's tools, interface, or experience.