Except in this case no one got a correct answer annulled because it was impossible to give a correct answer. At most people could have avoided the guessing penalty by not answering the question. Everyone's absolute score should have gone up, though since the SATs are normalized your score can go down if other people's scores go up more.
They should have given out a normalized score like 8.1/9 in this case.
30 points is a lot. I had a perfect score (1600/1600). Getting a 1570 would have been significantly different. This is probably worse at admission cutoff thresholds.
You would still have a perfect score after the question was annulled. It's just the difference between getting (for example) 33 out of 33 questions correct, or 34 out of 34 questions correct.
Well what's interesting about it is that a perfect score would be unaffected, but anything less would be affected because wrong answers are now weighted more heavily than before.
Although I'm not sure how the SAT assigns the scores - I don't think it's as simple as a percentage correct (otherwise the score would simply be out of 100), and that there is some kind of normalization they do? Can't remember... and it might have been different then anyway.