tedster - 5:19 am on Sep 24, 2012 (gmt 0)

My take on this is that somewhere out there someone has place a link to http://example.com/blue-widegets.htm

Exactly. For that very reason, you want to make sure that every URL that doesn't include a "www" gets redirected to the exact same file path, but using the "www" hostname. In other words, a redirect only for (or to) the root alone isn't really enough.

So I'd suggest you double check by taking a good internal "with-www" URL and requesting the "no-www" version. It should redirect as well.