I don't believe tipping is by any means standard on Acela or the other Northeast services.

The long-distance services that offer sleeping car attendants and waiters in full-service diners come from a different tradition. Those workers have in fact come out of a "tipping tradition." However, in my experience, many customers do not tip these workers.

Those services are by the way the heart of the Amtrak budget fights now, and the full-service diners may disappear in the near future.