Situational awareness and conflict de-escalation are skills that can be taught in a weekend, and don't need entire styles based on or centering around them. The bulk of Self Defense involves avoiding doing stupid crap and mitigating risks.
Ok, while I don't support the rediculous claim that a sport fighter can't throw thow the switch, I can't support this statement either. There are number of important differences between the average sport fight and a self defense situation.
The most obvious are issues of consent to fight and typically a period of escalation. In a sport fight, there is an immediate acceptance and consent on the part of both competitors. The hallmark of a self defense situation is that consent doesn't exist and that the defender needs to transition to it quickly. And while the fall back is usually "well, thats just common sense" then I have to ask why it seems to be lacking in so many quarters of the population.
Outside of intent, weapons, and environment, what is the difference? Fighting is fighting. Your arms don't become detached from your body requiring you to learn a different style of punching or grappling for Self Defense applications. You're taking the garnish (nuanced differences) and replacing the meat and potatoes with it.
Speaking from my subjective experience, I've competed in a Dog Brother's style full contact stickfighting event. In other walks of life I've been involved in non-fighting performance based events. I've also been attacked once in a bar. I can say that the adrenal dumps and phsycological conditions of the competition did not match those of the attack.
Were there similiaries? Yes. And note that I'm not arguing that anyone who practices a resistive, contact based martial art doesn't have a leg up on many MAists out there, let alone the general population. (also note that I'm not getting into dirty tricks, the str33t, or any other asinine arguement).
I am saying that saying there is little difference between a self defense situation and a sport fighting situation is a naieve statement.