Does Damon (or any other braces system) always widen dental arch?

Damon saying they grow bone and widen the jaws was a marketing scheme. All orthodontist have the ability to broaden the smile, keep it the same, or even constrict it using any type of orthodontic bracket system. There are several techniques to do this and they are used for each individual patient based upon what they need for the best result and is determined by the orthodontist treating them. While the Damon bracket is a good bracket, it does not do anything different or better than other bracket systems. 
If you are concerned about your smile being too broad, then address this with your orthodontist and he will determine the best way to get the result you desire.