In Roger's own words he's leaving Dodge because the chance to go to Ford was hard too say no to. Roger has never won won a Cup championship, and at his age I think him going to Ford to be aligned with Roush-Yates, or is it Yates-Roush, will be his best chance to win that Cup championship. Roger also said in an interview that he was looking for a long term commitment which he got from Ford. Maybe that does mean Dodge is year to year, or maybe with the new owners at Dodge, Fiat, they couldn't commit to anything more than a year or two, but that may change once the new ownership gets settled in.
Speaking of Dodge and Fiat I don't know if you're familiar with the new Dodge Dart, but it's based off of an Alfa Romeo car platform that Fiat is already producing. Fiat literally sent hundreds of finished Alfa Romeos from Italy to a plant in the Detroit area to be converted to Dodge Darts. I guess this was the quickest way to get the new Dodge Dart to the market, but in the future they'll be finished into Dodge Darts on the assembly line.