Sorry, you're right.
Enabling Remote Admin does open port 80. I am surprised that port 80 was used for Remote Admin. Would have thought it would be a more obscure port. But it is for your own Remote Admin so you would know the pwd to enter on the login screen.
Nevertheless,
even with port 80 closed you can still browse to your own IP and get the router's admin page, which is OP's point.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC