That is not necessarily the case. The client may well have restrictions on what technologies you use, especially if they are to run and maintain it after you have built it. This probably is considered part of the product.
But you and the client negotiate and come to an agreement or decide not to do business. If you fail to come to an agreement with many clients this may affect your reputation, but no central authority will ban you from talking to future clients.
If I started "Daniel's Ruby Shop", collected money from clients, and paid it to you if you made Ruby websites that met standards I set, and required you to Skype me at specific times or forever be banned from "contracts" you're not an independent contractor, you're my employee.
