Prolly a hidden condition Apple must agree to, to be able to use the AIM service with iChat. Like something to the effect of "No profiles" and "no animated buddy icons". You gotta remember that iChat is the only program that supports a chat service it's maker (in this case Apple) does not own as well. AOL makes money on those AIM ads, you don't think they can let Apple get off scott free do ya?
Someone's bound to mention Adium and Fire and so on, well these programs do not get AOL's, MSN's, or Yahoo's permission to use their services. Which is why everynow and then the compatibility with those services are broken, and users must wait for a patch.