I don't doubt it's effectiveness at keeping spammers out. But when building a spam filter you also have to keep in mind the false positive rate. By excluding anyone who don't have the time or inclination to spend time grinding for rep on SO, they're excluding a great deal of knowledgable people.
Fortunately, on the functions that matter, they blow their competition out of the water. Before SO came around, I dreaded seeing Experts Exchange links in my search results.
Given how long SO has been around, however, I would value a UI refresh over chat.
If they aren't willing to answer or ask a question to use a chat room structured around answering and asking questions, I think I'm okay with the situation.
I'm not saying it's not too much of a hassle -- of course that's up to you.
I would estimate that there's a vanishingly small number of people who are completely unhelpful in Q&A but would be fabulously knowledgeable in chat. I mean, there's you, but I just don't suppose there are that many others. If it keeps out every spammer and blocks three people who would legitimately be helpful, that's probably the best filter ever.
So what you're saying, is that any spambot could thwart the system easily, and the arbitrary restriction is silly, and mainly just means this will not take off beyond fanatical SO users (Which is fine, if that's their aim).
IRC has developed fantastic ways to keep out spammers and idiots. And the methods don't usually involve things like this.
For perspective, it would be far easier to spam the front page of Hacker News, and yet most people agree that HN's system works pretty well.
* Log in.
* Find a question that you can answer, or post one.
* Wait and hope you get some points.
In the same amount of time you could have already hopped on IRC and received an answer.
My guess is that SO is currently big enough to attract viable communities for several of these "channels", but that many others will end up as ghost towns, and that, overall, IRC will continue to be 'bigger' for real time chat. It's probably a big enough space that this can be successful in its own right, even if it's not huge, although I think I will tend to prefer IRC.
Also, signing up for HN is way faster than having to ask/answer a question.
You'd probably get enough reputation from that question to be able to ask your next one on the chat rooms if you wished.