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.
I was very suprised that we are forced to use port 80, on my old netgear the default was 8080, but it could be changed to something more obscure.
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.
OP did not specify whether they were at home or somewhere else on the www, so I assumed they ment on the www.
Line: Length 250 metres
Modem router: Orange BrightBox
= Down 19418 kbps Up 1019 kbps
WBC 20Mbps Down: 22010 kbps Up: 1019 kbps
ADSLMax 8Mbps Down: 8128 kbps Up: 448 kbps