Is Robshaws workrate actually any higher than the alternatives? I recall in the 6N it was highlighted that far from being the workhorse, he was actually slow and not making as many tackles or hitting as many rucks as other forwards. We cannot have any dead wood going into the WC, experience only counts for something when you are still performing. The squad that won the world cup have tons of experience and a winning mentality, doesn't mean we would want any of them on the field now. Robshaw, Brown and Cole have all lacked pace around the park and are clinging on for "unseen work", "experience" or just being "reliable". If they can't deliver the things that are their reason for being retained then what reason is there to retain them?
Jones set out from the start to build a core of players in the team as all successful teams do that. The difference is in successful teams the core are there consistently because they are just better than the alternatives, they aren't there because someone has decided they need to be there.