Funny thing last week when I wrote a “Page Information Web Part” (something that showed something like ‘This page was last modified by X on Y’) and it didn’t update at all when Web Parts were added, modified or deleted.
I can see why it wouldn’t but I still think this is a flaw because there’s no way to see if the page was modified (ie. Web Parts added, modified, removed), not even with Versioning on.
A quick fix for me was to check in my Web Part if the page was just in Edit Mode and then call an SPListItem.Update() on it.