didn't msn messenger came with windows pre-installed?
this means that your non-tech savvy friends have an incentive to use it, just like the internet explorer.
"hey John, I want to chat with you over this internet thing"
John likes Jane and wants to talk to her but she is not comfortable with downloading and installing programs. She noticed that there is an app which name suggests that it is for messaging, she clicked the icon, answered the questions and created an account.
Now the tech savvy John has to create msn messenger account to talk to Jane. All the people missing from ICQ are on msn messenger now and those on ICQ can easily create a msn accout. At first both msn and ICQ run side by side but msn messenger has all the people from the ICQ while ICQ lacks many of the friends. Why bother to use ICQ? the starting sound is not good enough reason and the RAM is scarce resource for many. so, don't run ICQ all the time, only when you need it. Msn catches up with the features and people don't have reason to use ICQ anymore.
you can switch to some other network if you have somebody to interact there.
also, many hated ICQ. it had annoying spam, the messages you receive from people that are not on your list.
people can move away from facebook only if there emerges a network with a killer feature, builds up some core network of early adopters and the rest follows them because they know the people there.