I'm an extremly big fan of Sonic. I'd say my love for the two mascots are about equal. It was always akward for me back in the 16 bit wars were always akward for me because I was a fan of both the SNES and the Genesis.
As for the Eggman thing...Dr. Robotnik has always been called Dr. Eggman in Japan and for some reason the guys at Sega of America decided that Dr. Robotnik was a much better name for Sonic's nemesis. Dr. Robotnik has a much more sinister feel to it, I admit...But eventually, they decided to get Sonic a little closer to his japanese roots by introducing the concept of Eggman in Sonic Adventure 1 by initialy making it a nickname Sonic and co. called him. Then...They just started referring to him as Dr. Eggman...
This trend isn't too unusual, really. You know the Princess? Princess Toadstool? In Japan she's always known as Princess Peach. But here in America, she was always only known as "The Princess" Or "Princess Toadstool" until the day Mario 64 came out. Then Peach was introduced to the US Audience as the Princess' first name.
Another example of this is Final Fantasy adopting the original numbering system in America. Instead of Final Fantasy VII becoming America's FFIV, it too was labled VII.
I know if I desgined a character named Sketchy Sketchy and in Japan he was named Squiggly Man the Brave, I'd be a little disapointed.
Sorry, it's early in the morning-some of the history might be a little off. Sorry for rambling, too.