I just googled to find market share in the IM market and fonud this:
I don't know how accurate those numbers are, but that is what I have. Now, why would Microsoft want to use the protocol that is used by the player that has like 1% market share? Where is the incentive to using an open protocol when they only add 866,000 potential customers. If anything, MS did the right thing makeing Messenger interoperable with Yahoo. Isn't IM about the users, not what communication protocol that powers it?