Are remote software teams more productive than what? Than local software teams? That is an impossible question to answer without knowing much more about the teams, isn't it?
OTOH as a person running a software business with different types of teams (I have local, I have remote teams) I can say that as long as there is somebody in the remote team capable of understanding the requirement at the business level and capable of managing the team there shouldn't be any reasons for the remote team to be less productive.
Unfortunately as all things in life this also is not as simple, it is very difficult to ensure that the remote team understands the business really well, so rather than trying to achieve the unachievable you have to give out requirements in short, easier to manage portions and you have to coordinate daily.