Nope, they're dominated by a few because when a specific company becomes successful enough it can buy out the rest of the players.
The large firm can't just buy up all the small firms either because new firms are started all the time, and if every person who starts a small firm is rewarded with a buyout, the industry will attract more and more new firms until the large firm can no longer afford to buy out new firms. --------------- Examples of industries that not dominated by three or four large companies: mining, farming, house cleaning, and being a land lord.