The difference is important in comparing to other online shopping portals. For example, if you order from Barnes and Noble at:
http://bonuspointsmall.com using Platinum or Centurion card you will earn 1+2=3 points per dollar, one point for the financial transaction plus two points for using the site.
http://advantageshopping.com using any rewards card you will earn at least 1+3=4 per dollar, at least one point from the card issuer for the financial transaction plus three AAdvantage miles for using their portal.
http://thankyoumerchants.com using any rewards card you will earn at least 1+3=4 per dollar, at least one point from the card issuer for the financial transaction plus three Thank You points for using their portal.
I think the American Express terminology is misleading because they are
including the base point earned for the financial transaction, while other sites advertise only to the points earned for using their site because they allow you to use any card to pay.