Agree. And the articles refers to other emerging tech entrpreneurship hubs (secondary markets) that make it possible to start a company and take advantage of the established ecosystems.
If you are not in a city where such ecosystem exists, you could probably start building a prototype there but as soon as you need to scale up (financially, hiring, or other) you will probably need to start networking or moving a city that has one.
Yes. Mark Suster has said that you can grow to ~100-200 engineers in LA but it would be hard to go much beyond that. Groupon can hire all the writers and salespeople they need in Chicago but they opened a development office in Palo Alto to get access to a bigger developer pool.
If you are not in a city where such ecosystem exists, you could probably start building a prototype there but as soon as you need to scale up (financially, hiring, or other) you will probably need to start networking or moving a city that has one.