Firesheep is just an automated GUI for what we've been doing all along. Ettercap, wireshark, etc are far more flexible and can be used to execute a wider variety of attacks. Firesheep, for example, won't ARP poison on a wired network.
But Cain is in my standard pentest toolset for various reasons, not just ARP spoofing.
Right... which is why he didn't mention wireless networks...
That's like saying, yes SQL injection is powerful, but it doesn't work on CSRF vulnerabilities -- complete non sequitur.
I mean, I even explicitly mentioned Ettercap, which does ARP spoof. Is there a way I could have made that clearer?