That's interesting because the only people I know that use AIM are the ones I've met here. Everyone I know is on MSN and Skype.
Other than a few porn webmasters I know, my ICQ is dead now too. Out of the 50 or 60 people I had on it years ago, maybe 6 are still using it regularly.
Do you have any real question? Use something like Adium or Trillian to keep multiple messengers + accounts and stfu. You guys have too much time on your hand to discuss stupid shit like this...
It's just an industry standard. In a business like this where so much communication is required it is easier for everyone if we all use the same thing, and because people have been using AIM for so long people don't really want to change.
Like how porn webmasters all use ICQ... ICQ sucks, really badly, but most people who started in porn early on started using it and they've used it for 8+ years, it would be pretty hard for the whole industry to collectively decide to change all at the same time when what they use is already working
AIM does the job for me, I use Pidgin so all IM clients look the same anyway. Although, Skype would be a far better alternative.
I've also noticed AIM is really an American thing. There's not a lot of people in the UK outside of AM who would want to use AIM (mainly because those people have tried the client and it sucks majorly), it's always been MSN messenger here.