Ford & GM do not release new product lines at the same times. A good example of this is the Mustang & Camaro. If you recall, when the new Mustang arrived in 2005 there was no Camaro. The Mustang was a real seller for Ford, until the new Camaro arrived, which began to outsell the Mustang. Ford is releasing an all new Mustang for 2015, while GM is still using it's current body style. I expect Mustang sales will go up. It's predictable.
Ford and GM however both have new body styles, but the 2014 Chevy has been out a little longer than the as yet to arrive 2015 Ford.
What would of been more exciting and more box office like is if Chevy and Ford released new trucks the same year.
But then they couldn't goose up who sells more with BS.