Twitter introduced SMS authentication as a second factor. Do you really think that their number of fraudulent logins for users protected by that second factor hasn't gone down to near zero?
I do agree that 2FA, even with cell-phones, will improve the security of the web interface. The CloudFlare breach was caused by using the phone as an independent authenticator (overriding the password) which is not 2FA, as I understand it.
And I agree, the likelihood of SMS interception or spoofing during the verification process seems pretty slim. I'm going to bow out to the security experts at this point.
Granted, this requires physical proximity though, which definitely raises the bar for any attacker.