Don't worry, they are not losing money on your trade. Used pickup trucks are in high demand right now, especially late model ones with relatively low mileage.
When I bought my 1500 last year you could get a brand new truck with 10 miles on it for less than a 2-year-old truck with 25,000 miles on it. In January! A no-brainer if you ask me. Yet, there are apparently people who will pay those outrageous, near-new prices for a used truck because they think they are saving money! Dealers love to see these people walk up because they won't even price out a new truck to see how much the dealer will knock off list price.
Keep an eye on the ads for that dealer and see how much he's asking for your old truck.