Your overestimate the value of AIM. The reason you don't have to broadcast your AIM address in a public forum is because you can use your email address for that. Your email address takes the spam beating, and then those select few contacts who establish themselves as valuable get the upgrade to your AIM buddy list.

Now imagine there's no email. How do people get your AIM address? Your friends can contact you but what about everyone else? Do you post it publicly? If not, you would lose out on many potentially valuable relationships because it's harder them to make first contact with you.

In summary, IM only works because of its blue-collar friend Email, who handles all the street fights so that IM won't have to.