Part of the "problem" with myspace and "fans" is that in many cases people are joining sites of friends of friends, etc.
So when someone is the millionth person to join, they may or may not be a fan of that artist.
By joining "your" site, that person also has another friend on their site. That's how social networking sites work (duh)
Someone getting an email saying you are the 20 millionth fan and have won a prize maybe a bit of a "huh? I was added to 40 sites this weekend".