This is purely anecdotal, but I found it interesting nonetheless. Craig Hockenberry posted a chart showing a (relatively) big Christmas Day spike in downloads of his free Clicker Apple Watch app.
That graph shows the last month of downloads for my free Clicker app for watchOS. Since this app does nothing on an iPhone or iPad, the only reason to get it is if you have a new watch.
Makes sense to me. [H/T John Kordyback]