If that's a flaw, most IM clients suffer from it. Adium and others were designed for the sole issue of interoperability, but they still require you to have accounts on each system. True interoperability, like demonstrated with iChat and AIM or Yahoo and MSN, only require one account. Oh, for the day when you only need one account on one system to chat with all others on iChat, AIM, MSN, Yahoo, Skype, etc.
THAT day will never come.
on the contrary, that day will definitely come. remember the early days of consumer-oriented internet? when people used services like AOL or Prodigy, and there was little-to-no inter-communication possible? now you can e-mail from any domain to any other domain seemlessly.
there will eventually be total interoperability of iChat, AIM, MSN, Yahoo, Skype, etc., where all you'll need is an account with one of them and then be able to communicate with others. if we see true integration in the iPhone as a pioneer and then later devices in the future, we might be able to call iChat, AIM, MSN, Yahoo, Skype, from Verizon, Cingular, T-Mobile, etc. (just U.S. based service providers as examples, but you get the idea).