> How much has the Internet done for your business that a smaller, proprietary network wouldn't have?

Why do you think other networks wouldn't have grown global?

> If there are three or four proprietary networks with limited and expensive communications between them, growth is hobbled.

I agree, and there was tremendous pressure to interconnect them. The "inter" part of internet is the result of that, it's why it's called the internet rather than Arpanet. Numerous packet switching networks were developed in the 1960s, not just Arpanet.