I don't know all the legal details, but...
My understanding is that the copyright date indicates when material was first published in its current form. For a book, that is the date of first printing of the current edition.
Most web sites seem to treat the copyright as applying to the site as a whole. so the copyright date shown on ALL pages is the last date ANY page was updated.
I believe most people who see a copyright date on a web page assume it applies to the whole site. So, when they see a 2008 copyright date, they conclude that the page was last updated in 2008.