The argument is a "the technology isn't there yet and spammers are running rampant, so the obvious solution is block it, which isn't ideal", not "Google is doing this because they want a monopoly on chat, and broke the protocol to do it".
Doing this strikes me as throwing the baby out with the bathwater.
But before they start on this research project, they might want to do something about the spam their users are getting now, right?
What is it with modern times, where people are willing to sacrifice fundamental things, like applications that adhere to standard protocols, to gain some minute level of relief from something that's just "annoying"?
They're not stopping anyone running a personal ejabberd server.
One of the first things that one thinks of when designing/projecting a large-scale system should be the potential for abuse. Are you trying to convince us that Google didn't take that into account when they chose XMPP as the underlying technology for GTalk?
Imagine spam filtering based only on the purported sender address. It'd probably suck.