So, 3+ years after the original post and this issue still has not been resolved.  I am starting to wonder if switching from Xero to QBO was a good move.  This is pretty simple (or it should be.)  I edit the Standard invoice template (Invoice > Edit > Design > Manage) and click the Edit link on the "Standard" custom form style.  Click on the "Content" button and then pencil icon on the the bottom section.  Edit the text to be displayed and click the green "Done" button.  Any new invoices that are created manually do include this text.  Any invoices impoted via CSV do not contain this text.  This should be standard and not requite an "Enhancement Request" from development.  Help us out here, Intuit!