As a long time practitioner of Tai Chi I am not surprised by this at all. The major benefit that it brings is the very slow movement and moving with softness and strength exercise body and mind together. It is like a kind of neural programming. I believe that the years I spent practicing Tai Chi and Chi Kung have helped me avoid many potential falls, and to move easier. It has been a real regret that I can no longer stand on one leg easily, but I won't give up this great tool ever, as it keeps me on my feet and moving. The heel - toe walk that is so important to PWP's is a fundamental part of what you learn, and it is this that helps prevent falls, by ensuring that you don't walk with dropped toes.
It also strengthens the side muscles of the legs that are often neglected in other forms of exercise - these are the ones that are used in turning, and the first muscles to go as we age, turning is again where there is a risk of falls. It does this by teaching you how to turn safely and smoothly, and how to shift your weight from one foot to another. It is really great for those of us who have to think about how we move, because it gives a language to use as we do so!

Sorry about the ramble, I just got way enthusiastic at 3 in the morning!

Lindy