While I can't speak for the authors, I personally have been building out some sample apps with Tornado + Backbone. Since as it's working out Tornado provides a very scalable data layer with a minimum of fuss.
As someone who literally started using tornado a few days back, I can completely agree about the minimum fuss part. Though documentation is a little sparse atm, it has a fairly small code base. I was a little surprised it didn't come with a sessions module.
IMHO - Sessions don't make sense at scale. When you have sessions you usually cache objects in sessions, which means you need complicated update mechanisms. Better to store the objects in Redis and just have a single update...
