Well, exactly. It can be a HUGE scale of difference. Say you have an endurance race, or some long 10 plus lap races. That restart button becomes a second thought, where-as a rewind feature have little sacrifice cause it's only one corner versus the whole race. In real life, when you mess up, you either start over or lose the race. In GT, it's how it is now in a race series. You can't restart a race, and risk losing points for it.
I'm fine with rewind feature, but only in practice/free run mode. I want to be able to finish races without having to deal with the feeling of wanting to use it.
Not a strong reason, but that's my take.