Davis, you've got it. Many steam specials are in reality Amtrak specials (notice the P42 always behind MILW 261). That's because Amtrak has a large insurance contract so they get great rates. Friends of 261 probably carries 500,000 seat miles/year while Amtrak probably has 5 billion seat miles/year. Ergo Amtrak gets far better rates, and steam/fantrips (either on-network or off) are usually contracted thru Amtrak for insurance reasons.
The new Acela: It's not Aveliable.