There is no doubt, the dash cam market in regards to number of sales and usage is far behind the rest of the world. As it is,
@Vueroid is poised to make a large dent in this growing market, I have no doubt of that.
The market should not be looked at as number of dash cams across the population but the number of legally registered drivers that are using dash cams. This is a more relevant number as a family of 6 may only have two drivers if all children are under aged. Here is a reasonably done survey, by a lawyer, that shows %16 of American drivers use a dash cam.
Marc Brown - Statistics
In the U.S. there are approximately 242 million licensed drivers
Hedges and Company
By those number there is roughly 38,700,000 dash cams installed in vehicles. Those numbers as far as I know, are non-commercial cases, add in the commercial use and the dash cam usage goes up.