VanWagenen does say that apps have been getting better as time goes on. Though the Brigham Young study was just published, the apps her team reviewed were offered by the iTunes app store in 2009. It takes time to do a study and get it published. Many of today's most popular apps weren't yet available.
And, VanWagenen said, many developers are stumbling into some good use of theory whether they know it or not. For instance, sites like Fitocracy plan to up their game in the near future by placing a lot more value on user feedback. Their long term plans include "crowd sourcing," techno-speak for pooling and analyzing aggregated data so they can spot trends and report them back to their users. They could mine the data from say, Fitocracy members who lose the most weight over a six-month period, and then use that information to lay out a diet and exercise blueprint for new users with the same goal.