At Denver, the Zephyr is usually given a window washing by workers with long-handled squeegees. But on my recent trip that did not happen. I'm not sure if it was because the train was 2 hours late getting into Denver (westbound) or because it was a Sunday.
When I rode the Canadian, it was given similar treatment westbound at Winnipeg.
However, I've never noticed an en route washing on the other long distance trains I've ridden. I've ridden the full length of the Empire Builder, Crescent, Cardinal, Capitol Limited, and Silver Meteor (and several of the state-supported and corridor trains).