I dont see a difference only that the suit jacket has a buddy and the sport jacket does not. This does not mean though that when I wear a suit jacket I wear its pants I will wear it with another set of trousers also for casual wear.
Seems there is no hard right or wrong to this equations of the difference of them except some buttons. Length, fit, etc. are the same on both for me that I have if you were to seperate them by name.
So is there truely a difference?