No, the other objection is that this feature requires not only every user to own a cell phone but also to always have them on them, charged and on when they log in wherever they are. Edit: unless this is strictly opt-in which the suggestion didn't --and still doesn't-- specify.

Also, I'd like dear people with knowledge to tell us if adding this kind of extra level of security really works and whether it has adverse-effects such as people thinking having a less secure password or never changing it or whatever is fine then.