Thinking about it a bit more I think that while the cost savings of all of the relivery/rebranding might be small in practice the perception from the public would be that the cost saving is large. Therefore you get an easy win in PR terms because you are trying to "share the pain" with the public.
On a branding point of view I think it would allow the routes to become a "brand" rather than the operator. It would make it easier for the public to understand the complex system of operation we have in this country. If you knew, for instance, that a London train from Darlington was silver, a Manchester train blue, a Middlesbrough train purple and a Birmingham train red it would be much easier. You could perhaps but a colour box in the route section of the ticket to avoid any confusion over allowable journeys.