Do you not expect attendants on these trains? And since your train only travels at 90mph you will need a larger number of dining cars and their associated cooks and waiters/waitresses.
The whole point is to offer sleeper accommodations. That requires more people to clean up/prepare the train for the next trip, but not (many) more for the actual operation while running. Although the goal is to get more people to take the train by making it more attractive as an option, the direct comparison is for the same number of passengers: take advantage of the flexible length of trains to provide a more compelling travel option, but with the same number of people. So no greater number of dining cars etc. -- unless you're pointing out that not everyone gets dinner on a regular trip, in which case sure, I guess.
