>> "Your value is in the protocol itself, not where it's being used."
Can you name any open protocols that are profitable businesses? I don't think writers of the email RFC made all that much money out of the email spec :/
The protocol doesn't have to be open for everyone forever. When these feeder companys begin profitting, and when Twitter determines the time is right, they can charge for acess to the protocol.
The 3rd party clients can all just get together and setup their own backend. Most people are using 3rd party clients anyway.
If a few influential people with tons of followers were using twitter client X, and that client decided to stop using the twitter backend, and instead use something else, you'd likely see a mass exodus (As long as the client was good enough and available on multiple platforms etc).
I guess my point is that the valuable bit, the bit people care about, is the client, and who they can access from it. The network, protocol, backend etc, meh.