Wow this is an old topic.
I would like to change my opinion on the topic, and highly recommend "Tug of War; Modern versus Classical Dressage" it is a great read.
I do believe that some horses might benefit from a slight hyperflexion, but todays riders have taken it much too far; working for 10, 20, 30 minutes in hyperflexion. Not good for the horse at all.
Regarding the study - was the maze testing both directions? A horse might choose one arm over another for different factors, such as the arm in relation to the barn, the arm being the horse's "better" side, the arm being towards the "out" gate?
I am very skeptical about studies, especially ones posted in mainstream magazines.