Hi Dave,
It looks likely that there was no activity to report. As you know, it skips activity by you. If nobody else made edits to profiles in your Watchlist, no Activity Feed update will be sent.
This is the activity in your Watchlist: http://www.wikitree.com/index.php?title=Special:NetworkFeed&who=Rutherford-448
I know that means that you don't get the birthday update every week. We've thought about changing that system, i.e. sending an update if there are any birthdays, even if there is no activity. Currently it's viewed as a little extra thing, not the main reason for the update.
Chris