Having just booked an AT trip and reading the new refund policy I think sleeper passengers are treated much worse then coach passengers.
It's far easier for [Amtrak] to sell another coach seat last minute than another sleeper space.
Source?
My posterior, mainly.
I don't have a real source but instead formulated a hypothesis based on my assumptions of everything from Amtrak riders' preferences to Amtrak yield management strategies to observations of the way other businesses run things. To use an exaggerated example, consider a busy restaurant that has an attached banquet room that they use for wedding receptions and the like. It's likely that if you make a reservation there and then cancel last minute or no show, you won't face any repercussions nor be asked to back up your reservation with a deposit or anything. They might be mildly annoyed, but they have many seats at many tables, and the table that was to be used for you will probably be used by someone else. However, if you want to reserve the banquet room, you'll be more likely to have to put up a deposit or something, because while you have it reserved, the restaurant has to turn away any other potential customer who wants it for the same evening. If you then cancel at the last minute, they're less likely to be able to fill that space because not only do they have a smaller inventory of banquet rooms, you've got a smaller pool of potential customers to sell it to since it costs so much more to rent the room than just eating at a table at the restaurant.
Another example: I like to cruise a lot. A lot of lines have a different deposit policy or cancellation policy for the higher end suites than for the majority of staterooms. Same principle applies. There are fewer of them, they cost a lot more, once they're booked the line has to turn away potential customers, upon a last minute cancellation they have to scramble to find someone willing to pay the extra. Sometimes they can and sometimes they end up discounting heavily just to fill it. They'd rather not have to discount, so once they've landed a paying reservation, they use policy to try to keep it.
I don't know whether sleeper passengers are less likely to consider a last minute trip than coach passengers, but that could play into it as well. Of course the Auto Train could have a different ratio of planners vs procrastinators than the rest of the system, but I would think the other principles still apply equally well there.
So, no hard source, but there's my justification for my position. Let it be known by anyone else reading my earlier contribution to this thread that my views are purely conjecture, represent my own opinion, and perhaps bear no similarity to reality. That said, if you or anyone else has any information, sourced or otherwise, that contradicts my position, I'd love to hear it!