@croydon - It's really interesting studying the behavior of markets and businesses, as you would think by this definition that it would actually be more difficult to start a business in a field where there were a lot of minor competitors, rather than just a few big ones. In fact, often the opposite is true.
I guess you have to take into account that the big companies will be able to price under the small companies and will also be able to afford to stay up to date with any new technology as well. Plus brand loyalty is very important and big companies are often more well known and able to advertise. I wouldn't want to start a new cola company in competition with Pepsi or Coke, for example.