I've got a to do item in our project tracker to add fields for those purposes to page settings.
Note that the purpose of the existing field was not really for tracking who modified the page settings, it was for tracking which pages have new content, but since pages don't directly have content attached to the page object but only via features loaded on the page, that timestamp could be updated by any feature upon editing the feature content ie the html content feature whenever its own content is updated would also update the timestamp on the page that contains it.
So I will be adding 2 new fields to actually keep track of change to page settings. I totally agree we should have those fields.
Best,
Joe