A type of Obfuscation, that allows for more security for the Admin password. First, you could never tell your browser "remember the password for this site", because the browser only sees the password you're suppose to enter. Second, God forbid, that you should have a keylogger running under you, however that would also be outwitted.
Malicious minds that plot all kinds of internet anarchy, have made it necessary to obfuscate almost all of our source code to protect it from reverse engineering, malicious code insertion, and IP theft, so I'm not surprised to hear that's it's filtered it's way down to the router login screen. (though it's kind of sad).
I still remember having to flip dip switches on an 8086 before I typed in my 1000 line basic program, so I could play the game it contained. And later, how no-one secured their routers, even though the option was available. Those were the good old days, but I wouldn't go back for the world!
For those curious types, there are those simple utilities out there that will reveal what's under those little black dots.
