junebug - Unfortunately, I believe that is fundamentally untrue, and perhaps a misunderstanding of the crew. For example, a train with x-coach seats and y-sleeper passengers will not have x-y seats available on a sold out train. A sold out train means just that - all coach seats will have someone in them between sold out stations, and all compartments that are open for revenue are occupied (with or without the max pax per compartment).
In other words, if you are a sleeper pax on a sold out train, don't expect a coach seat to be available to sit in. The base fare (before adding in the sleeper supplement) is NOT a coach ticket. It's a rail fare.
I don't really see much reason for a Roomette passenger to go to coach. The view is the same and the seats are larger and more comfortable. Plus, a table opens up for your laptop/crossword/etc.
Now bedrooms are a different story - the seats don't necessarly set up with the best window view.