BTW - For anyone that is interested this feature of adding and editing blocks for the Site Homepage (including the ability to add a sitewide block) does NOT work if you have a user's front page set to their "My Moodle" page.
This setting is adjusted in the Appearance/Navigation part of the admin menu. Once you change the "Default homepage for all users" setting to be "Site" instead of "My Moodle" THEN you can adjust the blocks on the site front page.
Should this be considered a bug?