Well, I think there are different types and methodologies of meditation that are believed to work. My guess is studies tend to focus on one format to be consistent and build on each other. Meditation at its core is nothing but practicing focus and self control, so my guess is a whole range of 'games' is possible to achieve the same effect but sitting down and focusing on your breath is basically the most practical. I have not played the brain games and so can't comment on why they appear not to achieve the same effect - perhaps they put too much focus into the abstractions and visuals of the game, and not the introspection of meditation.