In the real world, some people I meet greet me by name, others don't. And there is a certain correlation with how well people know me, because only those that know me well enough to actually connect my face to my name can greet me using my name. I'm not running around with a huge name tag. Recognition in the real world is mostly visual. If I changed my name, the same people would still recognize me.
The virtual world doesn't work like that. If a new guy is invited to your guild you get a message saying:
[Djoe] has joined your guild
[Guild] [Djoe]: Hello guys!
and you can greet him with "Hello Djoe" without ever having even seen his face. You would have no idea if Djoe was previously called Phred, even if you had read on the forums that a guy named Phred had quit his previous guild taking the contents of the guild bank with him. And facial recognition doesn't work in MMORPGs, because first of all there aren't so many different faces in the game, and second the face is relatively tiny on your screen. If you met Phred a few days ago, and today you meet Djoe, still being a level 70 warrior but having meanwhile acquired a different shoulder armor and a new name floating over his head, you'll think he is a different person. There are too many similar looking characters around to assume otherwise. The name *is* the identity, and by changing your name you can easily change your identity. No FBI witness protection program needed.
If Phred never did anything wrong and just changed his name to Djoe because he liked the new name better and didn't think the consequences through, he'll be in for some nasty surprises. For a while he won't get any tells from friends, because they don't have his new name