The fact that nobody is watching the big three networks anymore has little to do with distribution channels and everything to do with the product.
Network TV does still have value and viewers. I personally don't watch the network news, it's the only thing I refuse to watch. The biggest PLUS with having networks from clear across the country is "time shifting". If I miss an episode of '24' on WNYW-NY, I can time shift an hour later and watch it on KDVR-Denver, or three hours later on KTLA-LA.