How many components need to be networked?

I have an A/V preamp, HDTV and Blu-ray player that are all network ready, and all of which seem to have access to the same types of service (e.g., Netflix, Pandora, Napster, etc.). Is there any reason that ALL of these need to be connected to the network, or will any one do the job?
One should it. The Upside is the ability to access those services from any one component once the service fee has been paid.