It's not about Yahoo and other big players. The edge GTalk had was it was capable of talking to my server and to my friends' servers.
Now that edge is gone, but it's really not needed any more, they have enough mass to not care.
This is exactly about Skype, Yahoo and others. Only a handful geeks and sysadmins use Gtalk as an XMPP relay to talk to. Losing these few edge cases has no impact at all on Google, however, MS and Yahoo being able to have an unfair advantage does have impact on Google (and by unfair advantage, I mean MS and Yahoo being able to talk to Gtalk but Gtalk not being able to talk to Skype and Yahoo Messenger).