Says so on their home page. Or somewhere else on their site. AOL likes to block Jabber servers. So while Jabber theoretically interacts with and "does" AIM, AOL blocks the individual servers. Therefore, Jabber cannot turn into my "all-in-one" IM client.
Hence my question about gaim (whereupon I've already set up 2 AIM IDs, 4 Y! IDs, and an ICQ ID).