Back in the Wessex days some of the Melksham were carting around fresh air so it's not surprising they were cut back to the mimimum if managers no longer needed to use these trains.

I think people are missing the point here.  While Plymouth is of histroric significance due to the navy base there, this is now in decline and Exeter is now the key city for the South West peninsula and I would expect be where the majority of people on a train for the Westcountry are heading for.

As the market will bare a higher price on that route.  For example from Swindon to Paddington there are no real alternative ways of travelling so people will pay regardless.